Physics Class Exposure and Lab Guidelines

So first we're going to go over the new guidelines. So they've changed how exposure is being defined. So now if you're 15 minutes or more within six feet of someone, whether you have a mask or not, That would mean that you're exposed. So for the purposes of contact tracing, basically our entire classroom would be have to go on a list if anybody got on the list. Does that make sense? So basically we can't continue with classes the way I was originally intending. So everything's sort of all up in the air right now but... We'll basically just be doing everything on Collaborate from now on. So the lectures will all be online. I'll go over what we're doing for lab as well. So I've rearranged the entire lab room. So only four, sorry, only six people will be in the lab room at a time. All right, so because we're only having, basically we really only have six setups for most of our labs. So you can't really do, you can't share a lab system if you've got, if you can't be within six feet of another person. So we're just going to redo labs so that there's just one person at a station. Basically, you'll come every four weeks and we'll just do two labs at a time. All right. So I guess in total. That'll only be about eight or so labs. Here, can I get you to grab these? Alright, so on the, I guess the weeks that you are coming for lab, you can come to class, but otherwise I'd like you to stay at home. Hi, are you here for physics? Yes. Okay. All right. Okay. All right. So any questions on the lab guidelines there? Or on the, what's going to be happening from now on? So yeah. It'll be alphabetical. So the first four students will do the first week. Yeah, I don't have that list made yet. And even if I had it made right now, I wouldn't be able to communicate with you reliably beforehand. So that's why we're not doing lab this week. What? Yes, it's going to be for the other lab as well. But how soon that happens, if you have a Friday lab, we might have the list made. And so you might meet on Friday. We'll try to get that information to you as soon as we figure out what's going on. Yeah? lectures and stuff, are they going to be pre-recorded or do we have to watch them live? You won't need to watch them live. They should be recorded while I'm doing them. I'm still planning to do them at the regular scheduled time. So for the weeks that you do have lab, you can come in here. But I don't want everybody coming to each of the lecture sections because then we have too many people. All right, so Collaborate is the Blackboard's video chat system, and the videos will be available later. All right, so any other questions there? All right, so today we're just doing review for the test. The test is not tomorrow. The test will be a week from tomorrow. So the third... will be the test. It's set up so it'll be available at 12 a.m. and then just get it done before 11 59 p.m. You'll have 75 minutes during that time to take the test, so once you start you'll have 75 minutes. They recommend don't do it while you're traveling because if you go between cell towers it can toss out your tests. Let's see. So the LockDown Browser instructions are in the syllabus section. So you have to download the browser. And once you have it downloaded, you're just opening, or basically, The browser you download is specifically keyed to our institution, so it basically opens at the Blackboard front page. And so you can log in normally, but basically the only thing you can do with it is take the tests. Yeah, just read through the rest of that stuff. So if you don't have a webcam, I saw this software that you can use to act as a webcam. So I was able to use my iPhone to act as both the microphone and the camera. So that's one thing you can try if you don't have a regular webcam. If you've got a workbook, that's another thing to look over. There are also questions at the end of the chapters to look over. The answers to the odd questions in the textbook are at the back of the textbook. So there are lectures posted, and the notes from the lecture are up there. I think we're missing the first hour of this lecture, so sorry about that. This also has the test review from last term. I think it's the same test, but maybe you'll get something else out of it. Yeah. So the homework's there. Oh, are they wrong? Okay. Oh. Yeah, so it should be updated now. But yeah, that will probably happen. just because when it copies over the test it doesn't change any or copies over the course it doesn't change any of the dates so having the dates being wrong is a common occurrence uh just send me an email and i'll try to get them updated it'll be the september 17th the test too no so these are all due the day of the test so september 3rd And then the next test is on September 17th. And so those homeworks will be, do that.. Sure.. September, yeah.. Yes.. Right. So is there anything from chapter one regarding Aristotle? It won't be on the test. That's more history stuff. But if you find it interesting, feel free to read it. But I'm not going to test you on that. Yeah. Like everything that we'll be working with, like all our sheets that we can kind of like... So we won't be having that many calculations. So as you go through the test, you'll get an idea of what sort of things you need to know. But like, yeah, you'll need to know like velocity and acceleration, but I don't think we do any unit conversions, at least not in this chapter. And so next week, next Wednesday. We'll just be doing basically the same thing. We'll go over another set of 50 questions, and then the day after on Thursday. So any other questions? I probably need to repeat your questions, because they can't hear you online. So. Onto the test. So number one, so as an object freely falls downward, which of these can we say? So it's not A. What can we say about the acceleration? So the acceleration is going to be constant. So as long as you're in free fall, you have a constant acceleration. If you had air resistance, your acceleration would actually be decreasing. But it's definitely not A. So the only one that's increasing here is B, the velocity. Yeah, I'll post it on Blackboard. So the questions are there now. I somehow set it up so that it... posted or it would have posted at the end of today I meant for it to post at the beginning of today but either way it's there now yeah so number two if you roll a rock at the end of a string on ice-cold pond it follows a circular path so if the string breaks the tendency of the rock is two. Okay, and so the inertia will keep it going in a straight path. Okay, so the only reason it's moving into the circular path is because of that string pulling it towards the center. Once the string breaks and no longer pulls it, it's going to follow a straight line. Right, so the string was accelerating it towards the center, but without that force accelerating it, causing it to change direction. it's always going to move in a straight line. All right, so then our gain in speed each second for a freely falling object is about, yeah, so that's the the 10 meters per second. All right, so our acceleration, that gravity, is that 10 meters per second squared. And so that just means that every second the velocity changes by 10 meters per second. So for a package falls off a truck, It's moving at 30 meters per second, neglecting air resistance. Horizontal speed of the package just before it hits the ground is... Is it zero? It's not zero. So after it hits the ground, you could say that after that collision it eventually comes to zero. but they're asking before it hits the ground. And so one of the key parts here is that they're talking about the horizontal speed. So that speed is not changing. So we have acceleration, but the gravitational acceleration is in the vertical direction. but the horizontal velocity stays the same, and so our horizontal speed would just stay at that 30 meters per second. Right, so if your automobile runs out of fuel while you're driving, the engine stops, but you do not come to an abrupt stop, the concept that most explains why is, so we'll look for the inertia. Alright, so last incident just before airplane crashes. Passengers jump out, falls only two feet to the ground. The passenger is... A. So we're looking for A there. So even though you're jumping out, you're still moving very fast. We will not be having lab today. So once we get the schedule figured out, that'll be posted. So if you have a name near the beginning of the alphabet, you might have it next week. But last name. Oh, I guess there was a d to that. So even if you study physics, that's not going to save you from jumping out of airplanes. All right, so Galileo's use of inclined planes. I guess chapter one would have helped you here. But so the the inclined planes, basically when you're in freefall you have a large acceleration and that's hard to measure. I guess we had a video camera that makes it a little easier but by using an inclined plane it's slowing decreasing yeah slow down as the acceleration. Right. Alright, so then, which of the following is not a vector quantity? And so it's the speed. And so what makes something a vector? It has both, yeah. So whereas velocity has a direction associated with it, speed does not. And so because it doesn't have direction, that's why speed is the answer there. So a car maintains constant velocity, 100 kilometers per hour for 10 seconds. During this interval its acceleration is... nope. Okay, and so our acceleration is the change in velocity over time. Alright, so because we have a constant velocity, there's no change. And so, because there's no change in velocity, we have zero acceleration. Is it testing the multiple choice? Yes. So 10, if an object falling freely were somehow equipped with an odometer to measure the distance it travels, then the amount of distance it travels each succeeding second would be... Right. So an odometer measures distance. And so the distance that you travel is getting larger. So in the first second, you're only going five meters and then 20 meters, 45. But it's the square of the time. So while your velocity increases by a constant amount, the distance more than is just greater. The second one. So 11, a hockey puck is set in motion across a frozen pond if ice friction and air resistance are neglected. Of course, we're hard to keep the puck sliding at constant velocity is. And so what we're looking for here, when they say constant velocity, they're saying that it's at equilibrium. I guess it'd be dynamic equilibrium. And so in order to have that equilibrium, the net force has to be zero. And so what they're trying to describe is there's no... frictional forces slowing it down. And so if there's no forces slowing it down, you don't need any other forces in order to keep it moving. Okay, so we just need zero for a four. All right, so 12 if a car increases its velocity from 0 to 60 kilometers per hour in 10 seconds, its acceleration is... All right, so again we need the change in velocity. So we're going from 0 to 60, so the change is just that. 60 kilometers per hour and then we're dividing by the time which is six seconds. So we've got the 60 kilometers per hour Divided by 10. All right, the units look a little weird, but it's just six kilometers per hour per second So a ball is tossed vertically upward, it rises, it reaches its highest point, and then falls back down to its start. So during this time acceleration of the ball is always... Yeah, so we're accelerating because of gravity. All right, and so on the way up the gravity is slowing you down. At the highest point you don't just stay there, you come back down. And then on the way down you're also speeding up and that's always a downward acceleration. So we'll par. travels around a circular track at a constant speed. What else can we say? Acceleration, yeah. Okay, so it's important to see the distinction between a constant speed and a constant velocity. So constant speed, so we're going around the circular track, we're covering the same distance in a given amount of time, but because it's a circular track, the direction keeps changing. So even though the speed, the magnitude of that velocity is staying the same, because the direction is changing, there's still an acceleration. All right, so do you have a question? Right, so the speed is staying the same, so you're like going 60 miles per hour, but as you were traveling different parts of the track, the direction is going to change. So you might be going north at one point, east at another point, but in order to change the direction you need acceleration. Now if you're just going in a straight line at a constant speed, then the acceleration would be zero. So the acceleration is not zero because the velocity is changing. The velocity is not zero because you're moving, and also the inertia is not zero. So we are, I guess none of these, yeah. All right, and so if a car accelerates from rest at two meters per second per second, its speed three seconds later will be about So we're just looking for a there. So our acceleration is the change in velocity multiplied by time. So our change in velocity is equal to the acceleration multiplied by the time. So because we're accelerating at two meters per second per second in three seconds, that will change our velocity by six meters. So an object covers a distance of 8 meters in the first second, and then 8 meters in the second, and again 8 meters in the third second. And so we're looking for its acceleration in meters per second per second. Yeah, and so what this is describing is just that we have a velocity of 8 meters per second, and it just stays at 8 meters per second, at least for those 3 seconds. All right, so because that velocity is constant, the acceleration is zero. All right, so at one instant, heavy object in air is moving upward at 50 meters per second. So one second later, its speed in meters per second is approximately... Okay, yeah, and so on the way up, we have a decrease in velocity. Right. Whereas if we had gone the other way, if we're talking about something moving downward at 50 meters per second, after one second, that would get it up to 60. So the ball is thrown upward. and caught when it comes back down. So in the presence of air resistance, the speed with which it is caught is always. And so to think about this, think about the times that it's going up and the time it's going back down. No. Okay, so at the very top our velocity is zero. All right, and so you start with some speed at the bottom and to get to zero at the top it takes a certain amount of time. But then as you come back down, it takes exactly the same amount of time. So because it's the same time going up and down, it's going to be the same speed. Did I do that right? Sorry. So in the presence of air resistance. So if there was no air resistance, it would be the same. Does it not equal air resistance of going up versus down? The magnitude is the same, but it's in the opposite direction. So the gravity is always accelerating us downward, but the air resistance is always opposing the motion. And so the air resistance is slowing you down on the way up, and it's also slowing you down on the way back down. All right, so whereas the gravity, we're losing energy or we're losing velocity on the way up and then we're gaining the same amount on the way back down, because the air resistance is always opposing the motion, we're losing more or we're losing on the way up and the way down. And so we have less speed on the way or on the at the end than we did when we started. Coach, last just because the air is this way. Right. Alright, so 19, it takes 6 seconds for a stone to fall to the bottom of a mine shaft. How deep is the shaft? So what happens after 6 seconds? It hits the bottom. Right. So what happens after 6 seconds? In those six seconds we get to a velocity of 60 meters per second. All right, so that doesn't mean that we're covering 60 meters, because we're starting at zero meters per second and we're getting up to that 60 meters per second. So when they say falls here, they mean that it's starting at rest. And so our average velocity is just the average of the zero and the 60. Alright, so if we have an average velocity of 30 meters per second, and that acts for 6 seconds, then our distance will just be 180. So I needed the initial and the final velocities. So knowing the initial and final, I found that the average was the 30. And so then I just did that average multiplied by the time to get the distance. Thank you Right, and so for those six seconds, we've got the acceleration of gravity, and so we're just doing the 6 times 10 to get the 60. Yeah, yeah. Right. And so for three seconds, so in the three seconds, we'd go from zero to 30. And so our average would have just been 15. And then we would have done 15 times three. which give us 45. So in each second of fall, the distance a freely falling object will fall is... Okay, so the five meters is the distance it falls in the first second, but we're talking about each second, so not just the first, but any second. Yeah, and so it's increasing. Okay, so projectile is fired straight up at a speed of 10 meters per second. What's the total time to return? So because we're starting at 10 meters per second... So the other information we know is that at the top it's going to be zero. So to go from the 10 meters per second to zero, it takes one second. But that's not our answer because we're asking... not to get to the top, but to get back to our starting position. So it takes one second to get to the top, but then another second to get back to the starting. All right, so car accelerates from rest for five seconds until it reaches a speed of 20 meters per second. What's the acceleration? So we're just doing the change in velocity. So we're going from 0 to 20, so the change is 20. So we're just doing that change in velocity divided by the time. So a bullet is dropped from the top of the Empire State Building, while another bullet is fired downward from the same location, neglecting air resistance, the acceleration. They're asking you to make some pretty big assumptions there. So neglecting air resistance. So air resistance is going to be pretty strong on a bullet after it leaves the gun. So what they're wanting you to think about is that it's not the bullets, the velocity that's important. The acceleration just depends on the gravity. So regardless of how fast they're moving, they're both going to be accelerating because of gravity. And so our acceleration in both cases is just going to be that 10 meters per second squared. So no matter how fast you're moving, the gravity acceleration is always 10 meters? Nearer surface, yeah. If you can neglect air resistance, yeah. So as long as you're able to neglect that air resistance, we can say they have the same acceleration. The bullet fired from the gun is going to reach the ground much faster, but its acceleration is going to be the same. So a ball is thrown upwards, neglecting air resistance, what initial upward speed does a ball need to remain in the air for a total time of 10 seconds? Is that total, so it goes from the time it leans and then hits the ground? Right, so it's going both up and then back down. So if the total time is 10 seconds, that's 5 seconds up and 5 seconds down. All right, and so to stay in the the air 10 seconds, so with that five seconds up, you need to start at 50 meters per second to get the total time of 10. All right, if you started at the 100, you'd be in the air 20 seconds. So 25 compared to a 1 kilogram block of solid iron, a 2 kilogram block of solid iron has twice as much. There's actually all of these. So the kilogram they tell you, that's the mass, so it definitely has twice as much mass. But because they're both solid iron, the iron has the same density, so they're going to have the same volume. or sorry not the same, the twice as much volume. And mass and inertia mean basically the same thing. So the more mass you have the more. So with twice as much mass you also have twice as much inertia. And so we're looking for all of these. An object maintains constant acceleration unless there's a change in... Okay, so the applied force... So that... Whoa! That's crazy. Okay, uh... It's gonna be all of them. Yeah, so applied force would do it, but also changing the air resistor mass would also do it. So something just fell off the table? Okay, uh, yeah I guess leave it on the ground. I'll send in a ticket to support. That's... I guess it's like an electronics cover or something. That's weird. Alright, 27. Strange as it may seem, it's just as hard to accelerate a car on a level surface on the moon as it is here on Earth. This is because... And so our resistance to change, that difficulty in acceleration, that's the inertia. And that's the same thing as the mass. And so it's just as hard to accelerate on the moon as the earth because they both have the same mass. No, the car has the same mass on the earth and the moon. All right, now it'd be easier to lift the car on the moon because its weight would be less, but the mass is going to be the same. Eight, a ride on a roller coaster containing six passengers takes three minutes. Neglecting friction, a similar ride with 12 passengers aboard would take... all right, so we're looking for the same time. Yeah, so the acceleration of the roller coaster doesn't really depend on the number of passengers. It's still going to go through the same highs and lows at the same speeds, basically. And so it takes the same time. All right, so then a Newton is a unit of force there. So in which case would you have the largest mass of gold if your chunk of gold weighed one Newton on? So we didn't really talk about the gravity of Jupiter, but Jupiter's gravity is larger than the other two. Does that mean there's more gravity? What? There's more gravity on Jupiter? Yeah, so at the top of the cloud cover, it's not a solid surface, so you're not standing on something. But the acceleration due to gravity at that point is still higher. OK, so. We're trying to figure out which has the largest mass, but we say they all have the same weight. All right, so our weight is equal to mass times the gravity. So the one with the largest mass is going to be the one with the smallest gravity. And so we can say that mass is equal to the weight divided by the gravity. So we know they all have the same weight, and so whichever one has the smallest gravity will give us the largest mass. All right, and so of these, the moon is going to have the smallest, so it would have the largest mass. All right, so another way to think about that. Because the moon has a small gravity, you need more gold to get up to a weight of one newton. Whereas on Jupiter, because it has a higher gravity, you need much less gold to get to that same weight. All right, so 31 10 kilogram brick and one kilogram book are dropped in a vacuum. The force of gravity on the 10 kilogram brick is... And so we're looking for the force of gravity. Now if we had asked about the acceleration of gravity, that would have been the same. But when we ask about the force of gravity, that means the weight. All right, and so the one with the greater mass is going to have a greater weight. Yeah, so, right. And so that term, that force of gravity, means the weight. And so the weight is the mass times the gravity. They have the same gravity, the same acceleration of gravity, but because they have different masses, they'll have different weight. And so the one with 10 times the mass will have 10 times the force. In a vacuum, is there still no more gravity, or no? So, a vacuum... Just gets rid of the air resistance. So if an object's mass is decreasing while a constant force is applied to the object, the acceleration... So this goes back to the Newton's second law. So acceleration is equal to force divided by the mass. So we're saying that the force is constant. But so if the mass is getting smaller, then the acceleration would be increasing. Sure. So the force stays the same, but we're dividing by a smaller mass. And so when you divide by something smaller, that makes the result bigger. So if we increase the force, that would increase the acceleration. But if we increase the mass, if we divide by something bigger, that would make our acceleration smaller. So in this case, because we're... decreasing the mass because we're making that bottom term smaller, that actually makes the acceleration bigger. Alright, 33 10 newton falling object encounters 4 newtons of air resistance. The net force on the object is... And so we're just taking the difference. So the 10 newtons is the weight of the object, and so that's acting down. As it falls, the 4 N air resistance will be up, and so the net force will just be the difference between those. 34 on the apple weighs 1 N. When held at rest above your head, the net force on the apple is... So we're looking for at rest, and so that's telling us that it's at static equilibrium. And so if we're at static equilibrium, the net force will have to be zero. What is known as static equilibrium? So there's dynamic equilibrium, where you're moving at a constant velocity, and then the static equilibrium means you're at rest. So heavy block at rest is suspended by a vertical rope. So again, it's starting at rest. Then when a block is accelerated upward by the rope, what happens to the rope tension? Alright, and so when you're at rest, those two forces will be equal, but in order to accelerate upward, the tension will have to become greater to cause that upward acceleration. Right. So to accelerate upward, the upward force has to be greater than the downward force. And so the upward acceleration just means that the tension will be increased. So 36, if a non-rotating object has no acceleration, then we can say for certain that it is. Right, and so the no acceleration means that we're at equilibrium, but we have two different types of equilibrium. I guess the mechanical is the... just the overall term probably better if the mechanical wasn't there all right so we can say for certain that it's at equilibrium But without knowing more, we can't decide whether it's static or dynamic. I set up the... Collaborate to go till 10. I'm not sure if it's going to kick us out. It's taking a little longer than I expected. So 37, you relax at rest with left foot on one should be a bathroom scale. So you have two bathroom scales. You've got one your left foot on one and the right foot on the other. And so the scales, what can we say about the readings on the scale? And so we're looking for C there. So they definitely add up to your weight but it's not necessarily equally distributed. Right, so because you're not accelerating up or down, I guess if you were jumping on the scales, if you're relaxed, So if you're at rest, then the net force has to be zero. All right, so two together have to equal your weight. but it doesn't have to be exactly one half. All right, so tow truck exerts a force of 3,000 newtons on a car accelerating it at 2 meters per second squared. What is the mass of the car? All right, so we can say our force is mass times acceleration. So we know the force. And we know the acceleration, and so our mass, we just do the force divided by the acceleration. And then the units are kilograms. So force of 1000 Newton is the acceleration of mass of 1 kilogram at a rate of 1 meter per second squared. The acceleration of a mass of 2 kilograms acted on by a net force of 2 Newtons is... Okay, so our acceleration is the force divided by the mass. So if we're doubling the force and also doubling the mass, the acceleration will stay the same. A rocket becomes progressively easier to accelerate as it travels upward from the ground, mainly because... If you don't know anything about rockets, this probably isn't intuitive, but the reason has to do with the fuel. So as you burn the fuel, because fuel has weight, because it has mass... You're basically keeping the force the same, but if you have less mass, you'll have a greater acceleration. Alright, a jumbo jet has a mass of 100,000 kilograms. The thrust on each of its four engines is 50,000 newtons. What's the jet's acceleration? meters per second squared. Alright, so acceleration is the force divided by the mass. The force here is not just the 50,000. So that's for one of the engines, but we have four of them. And then we're dividing by the mass, which is the 100,000. And so we get 200,000 divided by 100,000. And so that's two. So brakes on a speeding truck are slammed on and it skids to a stop. If the truck were heavily loaded so that it had twice the total mass, the skidding distance would be... So this is probably hard to think about if you've actually tried to slam the brakes on a truck, particularly a semi truck. So with bigger trucks, it's not as easy as just slamming on the brakes, because if you do that, then the trailer goes a different direction from the truck. But if you just add a single body to the truck, then the heavier load would mean that there's also a greater friction, a greater resistance with the brakes applied. And so if you have those simplifications, even with twice the mass, because there's also twice the force, you'd still have the same accelerations and so your distance would be the same. So doubling the mass would double the force, and that would lead to the same acceleration and the same distance. Or at least that's how they want you to think about it in that case. All right, so 43, an object released from rest on another planet, requires one second to follow a distance of six meters. What does the acceleration in meters per second per second do to gravity on this planet? Okay, and so the key there is that this is one second. So in that first second, the distance corresponds to the average velocity. All right, and so if our average velocity is 6 meters per second, that means that our acceleration is going to be 12 meters per second squared. And so two factors that greatly affect air resistance are... Okay, and so we're actually looking for A there, so it's the size, but then also the speed, how fast it's moving. Size and mass are the same? No. So the air resistance doesn't depend directly on the weight or the mass. So the air resistance itself just depends on the how much air you're pushing out of the way, so the size of the object, but then also how much you're changing the speed of the air, so the speed that the object is moving. All right, so when a falling object has reached terminal velocity, its acceleration is... Yeah, so this has to do with the definition for terminal velocity. So that was when the weight was equal to the drag, the acceleration was zero. Alright, so feather and a coin have equal accelerations when falling in a vacuum because... So we're looking for a d there. It's the ratio of the force, the weight in this case, to mass is the same. So the coin has a greater force acting on it, but because it also has more mass, it still has the same acceleration. All right, 47, an archer shoots an arrow. Consider the action force to be exerted by the bowstring against the arrow. The reaction to this force is... So this has to do action-reaction. You have... two forces acting between two objects. So in this case it's the bowstring and the arrow. And so if we have the bowstring acting against the arrow, the reaction to that is going to be the arrow acting against the bowstring. And so we're just looking for that combination again. So that's D. Skydiver falls towards Earth. Attraction of Earth on the skydiver pulls the diver down. What is the reaction to this force? So again, it's the Earth acting on the diver. So the Earth pulls the diver down, and so the diver should pull the Earth up. But if we look at the choices, that's not one of the choices, and so it's going to be E. Car traveling at 100 km per hour strikes an unfortunate bug and splatters it. The force of impact is... So when we have that impact between the car and the bug, it doesn't have the same effect, but it's not because the forces are different. It's because they have different masses. The force is going to be the same, but because they have much different masses... It doesn't really have any effect on the car, but it has a big effect on the bow. You get different accelerations. Like in the same direction? It would still splat. So different masses lead to different accelerations. You can think of this like in terms of the Earth and the Moon. So there's the same force the Earth pulls on the Moon, the same amount that the Moon pulls on the Earth. But again, because they have different masses, the Earth stays... relatively fixed in its position while the the moon goes around the earth. All right and so another way, so we've got another example, so two people, one twice as massive as the other, tug of war. So there's 12 meters between them when they start pulling on the rope and so eventually they meet and we're trying to figure out how far the heavier person slides. And so in terms of their mass, they're going to have different accelerations. So the lighter person is going to move twice as far as the heavier person. All right, so if we think of the the distance that the heavy person moves as x, Then the distance the light person moves is going to be 2x. And so our total is 3x. And so that equals the distance to 12 meters. and so the distance that the heavy person moves is just 4 meters. Alright, so that's all we're doing for lecture today. If you have any questions, feel free to email.

So for the purposes of contact tracing, basically our entire classroom would be have to go on a list if anybody got on the list. Does that make sense? So basically we can't continue with classes the way I was originally intending. So everything's sort of all up in the air right now but... We'll basically just be doing everything on Collaborate from now on.

So the lectures will all be online. I'll go over what we're doing for lab as well. So I've rearranged the entire lab room. So only four, sorry, only six people will be in the lab room at a time.

All right, so because we're only having, basically we really only have six setups for most of our labs. So you can't really do, you can't share a lab system if you've got, if you can't be within six feet of another person. So we're just going to redo labs so that there's just one person at a station. Basically, you'll come every four weeks and we'll just do two labs at a time. All right.

So I guess in total. That'll only be about eight or so labs. Here, can I get you to grab these?

Alright, so on the, I guess the weeks that you are coming for lab, you can come to class, but otherwise I'd like you to stay at home. Hi, are you here for physics? Yes.

Okay. All right. Okay.

All right. So any questions on the lab guidelines there? Or on the, what's going to be happening from now on?

So yeah. It'll be alphabetical. So the first four students will do the first week.

Yeah, I don't have that list made yet. And even if I had it made right now, I wouldn't be able to communicate with you reliably beforehand. So that's why we're not doing lab this week. What?

Yes, it's going to be for the other lab as well. But how soon that happens, if you have a Friday lab, we might have the list made. And so you might meet on Friday. We'll try to get that information to you as soon as we figure out what's going on. Yeah?

lectures and stuff, are they going to be pre-recorded or do we have to watch them live? You won't need to watch them live. They should be recorded while I'm doing them. I'm still planning to do them at the regular scheduled time. So for the weeks that you do have lab, you can come in here.

But I don't want everybody coming to each of the lecture sections because then we have too many people. All right, so Collaborate is the Blackboard's video chat system, and the videos will be available later. All right, so any other questions there? All right, so today we're just doing review for the test. The test is not tomorrow.

The test will be a week from tomorrow. So the third... will be the test. It's set up so it'll be available at 12 a.m. and then just get it done before 11 59 p.m.

You'll have 75 minutes during that time to take the test, so once you start you'll have 75 minutes. They recommend don't do it while you're traveling because if you go between cell towers it can toss out your tests. Let's see. So the LockDown Browser instructions are in the syllabus section.

So you have to download the browser. And once you have it downloaded, you're just opening, or basically, The browser you download is specifically keyed to our institution, so it basically opens at the Blackboard front page. And so you can log in normally, but basically the only thing you can do with it is take the tests. Yeah, just read through the rest of that stuff. So if you don't have a webcam, I saw this software that you can use to act as a webcam.

So I was able to use my iPhone to act as both the microphone and the camera. So that's one thing you can try if you don't have a regular webcam. If you've got a workbook, that's another thing to look over.

There are also questions at the end of the chapters to look over. The answers to the odd questions in the textbook are at the back of the textbook. So there are lectures posted, and the notes from the lecture are up there. I think we're missing the first hour of this lecture, so sorry about that. This also has the test review from last term.

I think it's the same test, but maybe you'll get something else out of it. Yeah. So the homework's there.

Oh, are they wrong? Okay. Oh.

Yeah, so it should be updated now. But yeah, that will probably happen. just because when it copies over the test it doesn't change any or copies over the course it doesn't change any of the dates so having the dates being wrong is a common occurrence uh just send me an email and i'll try to get them updated it'll be the september 17th the test too no so these are all due the day of the test so september 3rd And then the next test is on September 17th.

And so those homeworks will be, do that.. Sure.. September, yeah..

Yes.. Right. So is there anything from chapter one regarding Aristotle?

It won't be on the test. That's more history stuff. But if you find it interesting, feel free to read it.

But I'm not going to test you on that. Yeah. Like everything that we'll be working with, like all our sheets that we can kind of like...

So we won't be having that many calculations. So as you go through the test, you'll get an idea of what sort of things you need to know. But like, yeah, you'll need to know like velocity and acceleration, but I don't think we do any unit conversions, at least not in this chapter.

And so next week, next Wednesday. We'll just be doing basically the same thing. We'll go over another set of 50 questions, and then the day after on Thursday. So any other questions? I probably need to repeat your questions, because they can't hear you online.

So. Onto the test. So number one, so as an object freely falls downward, which of these can we say? So it's not A. What can we say about the acceleration?

So the acceleration is going to be constant. So as long as you're in free fall, you have a constant acceleration. If you had air resistance, your acceleration would actually be decreasing. But it's definitely not A. So the only one that's increasing here is B, the velocity.

Yeah, I'll post it on Blackboard. So the questions are there now. I somehow set it up so that it... posted or it would have posted at the end of today I meant for it to post at the beginning of today but either way it's there now yeah so number two if you roll a rock at the end of a string on ice-cold pond it follows a circular path so if the string breaks the tendency of the rock is two.

Okay, and so the inertia will keep it going in a straight path. Okay, so the only reason it's moving into the circular path is because of that string pulling it towards the center. Once the string breaks and no longer pulls it, it's going to follow a straight line. Right, so the string was accelerating it towards the center, but without that force accelerating it, causing it to change direction. it's always going to move in a straight line.

All right, so then our gain in speed each second for a freely falling object is about, yeah, so that's the the 10 meters per second. All right, so our acceleration, that gravity, is that 10 meters per second squared. And so that just means that every second the velocity changes by 10 meters per second.

So for a package falls off a truck, It's moving at 30 meters per second, neglecting air resistance. Horizontal speed of the package just before it hits the ground is... Is it zero?

It's not zero. So after it hits the ground, you could say that after that collision it eventually comes to zero. but they're asking before it hits the ground. And so one of the key parts here is that they're talking about the horizontal speed.

So that speed is not changing. So we have acceleration, but the gravitational acceleration is in the vertical direction. but the horizontal velocity stays the same, and so our horizontal speed would just stay at that 30 meters per second. Right, so if your automobile runs out of fuel while you're driving, the engine stops, but you do not come to an abrupt stop, the concept that most explains why is, so we'll look for the inertia.

Alright, so last incident just before airplane crashes. Passengers jump out, falls only two feet to the ground. The passenger is...

A. So we're looking for A there. So even though you're jumping out, you're still moving very fast.

We will not be having lab today. So once we get the schedule figured out, that'll be posted. So if you have a name near the beginning of the alphabet, you might have it next week.

But last name. Oh, I guess there was a d to that. So even if you study physics, that's not going to save you from jumping out of airplanes. All right, so Galileo's use of inclined planes.

I guess chapter one would have helped you here. But so the the inclined planes, basically when you're in freefall you have a large acceleration and that's hard to measure. I guess we had a video camera that makes it a little easier but by using an inclined plane it's slowing decreasing yeah slow down as the acceleration.

Right. Alright, so then, which of the following is not a vector quantity? And so it's the speed. And so what makes something a vector? It has both, yeah.

So whereas velocity has a direction associated with it, speed does not. And so because it doesn't have direction, that's why speed is the answer there. So a car maintains constant velocity, 100 kilometers per hour for 10 seconds. During this interval its acceleration is... nope.

Okay, and so our acceleration is the change in velocity over time. Alright, so because we have a constant velocity, there's no change. And so, because there's no change in velocity, we have zero acceleration. Is it testing the multiple choice? Yes.

So 10, if an object falling freely were somehow equipped with an odometer to measure the distance it travels, then the amount of distance it travels each succeeding second would be... Right. So an odometer measures distance.

And so the distance that you travel is getting larger. So in the first second, you're only going five meters and then 20 meters, 45. But it's the square of the time. So while your velocity increases by a constant amount, the distance more than is just greater.

The second one. So 11, a hockey puck is set in motion across a frozen pond if ice friction and air resistance are neglected. Of course, we're hard to keep the puck sliding at constant velocity is.

And so what we're looking for here, when they say constant velocity, they're saying that it's at equilibrium. I guess it'd be dynamic equilibrium. And so in order to have that equilibrium, the net force has to be zero. And so what they're trying to describe is there's no... frictional forces slowing it down.

And so if there's no forces slowing it down, you don't need any other forces in order to keep it moving. Okay, so we just need zero for a four. All right, so 12 if a car increases its velocity from 0 to 60 kilometers per hour in 10 seconds, its acceleration is...

All right, so again we need the change in velocity. So we're going from 0 to 60, so the change is just that. 60 kilometers per hour and then we're dividing by the time which is six seconds.

So we've got the 60 kilometers per hour Divided by 10. All right, the units look a little weird, but it's just six kilometers per hour per second So a ball is tossed vertically upward, it rises, it reaches its highest point, and then falls back down to its start. So during this time acceleration of the ball is always... Yeah, so we're accelerating because of gravity.

All right, and so on the way up the gravity is slowing you down. At the highest point you don't just stay there, you come back down. And then on the way down you're also speeding up and that's always a downward acceleration.

So we'll par. travels around a circular track at a constant speed. What else can we say?

Acceleration, yeah. Okay, so it's important to see the distinction between a constant speed and a constant velocity. So constant speed, so we're going around the circular track, we're covering the same distance in a given amount of time, but because it's a circular track, the direction keeps changing. So even though the speed, the magnitude of that velocity is staying the same, because the direction is changing, there's still an acceleration. All right, so do you have a question?

Right, so the speed is staying the same, so you're like going 60 miles per hour, but as you were traveling different parts of the track, the direction is going to change. So you might be going north at one point, east at another point, but in order to change the direction you need acceleration. Now if you're just going in a straight line at a constant speed, then the acceleration would be zero.

So the acceleration is not zero because the velocity is changing. The velocity is not zero because you're moving, and also the inertia is not zero. So we are, I guess none of these, yeah.

All right, and so if a car accelerates from rest at two meters per second per second, its speed three seconds later will be about So we're just looking for a there. So our acceleration is the change in velocity multiplied by time. So our change in velocity is equal to the acceleration multiplied by the time.

So because we're accelerating at two meters per second per second in three seconds, that will change our velocity by six meters. So an object covers a distance of 8 meters in the first second, and then 8 meters in the second, and again 8 meters in the third second. And so we're looking for its acceleration in meters per second per second.

Yeah, and so what this is describing is just that we have a velocity of 8 meters per second, and it just stays at 8 meters per second, at least for those 3 seconds. All right, so because that velocity is constant, the acceleration is zero. All right, so at one instant, heavy object in air is moving upward at 50 meters per second. So one second later, its speed in meters per second is approximately... Okay, yeah, and so on the way up, we have a decrease in velocity.

Right. Whereas if we had gone the other way, if we're talking about something moving downward at 50 meters per second, after one second, that would get it up to 60. So the ball is thrown upward. and caught when it comes back down. So in the presence of air resistance, the speed with which it is caught is always. And so to think about this, think about the times that it's going up and the time it's going back down.

No. Okay, so at the very top our velocity is zero. All right, and so you start with some speed at the bottom and to get to zero at the top it takes a certain amount of time. But then as you come back down, it takes exactly the same amount of time.

So because it's the same time going up and down, it's going to be the same speed. Did I do that right? Sorry. So in the presence of air resistance.

So if there was no air resistance, it would be the same. Does it not equal air resistance of going up versus down? The magnitude is the same, but it's in the opposite direction. So the gravity is always accelerating us downward, but the air resistance is always opposing the motion. And so the air resistance is slowing you down on the way up, and it's also slowing you down on the way back down.

All right, so whereas the gravity, we're losing energy or we're losing velocity on the way up and then we're gaining the same amount on the way back down, because the air resistance is always opposing the motion, we're losing more or we're losing on the way up and the way down. And so we have less speed on the way or on the at the end than we did when we started. Coach, last just because the air is this way.

Right. Alright, so 19, it takes 6 seconds for a stone to fall to the bottom of a mine shaft. How deep is the shaft? So what happens after 6 seconds? It hits the bottom.

Right. So what happens after 6 seconds? In those six seconds we get to a velocity of 60 meters per second.

All right, so that doesn't mean that we're covering 60 meters, because we're starting at zero meters per second and we're getting up to that 60 meters per second. So when they say falls here, they mean that it's starting at rest. And so our average velocity is just the average of the zero and the 60. Alright, so if we have an average velocity of 30 meters per second, and that acts for 6 seconds, then our distance will just be 180. So I needed the initial and the final velocities. So knowing the initial and final, I found that the average was the 30. And so then I just did that average multiplied by the time to get the distance.

Thank you Right, and so for those six seconds, we've got the acceleration of gravity, and so we're just doing the 6 times 10 to get the 60. Yeah, yeah. Right. And so for three seconds, so in the three seconds, we'd go from zero to 30. And so our average would have just been 15. And then we would have done 15 times three.

which give us 45. So in each second of fall, the distance a freely falling object will fall is... Okay, so the five meters is the distance it falls in the first second, but we're talking about each second, so not just the first, but any second. Yeah, and so it's increasing. Okay, so projectile is fired straight up at a speed of 10 meters per second.

What's the total time to return? So because we're starting at 10 meters per second... So the other information we know is that at the top it's going to be zero.

So to go from the 10 meters per second to zero, it takes one second. But that's not our answer because we're asking... not to get to the top, but to get back to our starting position.

So it takes one second to get to the top, but then another second to get back to the starting. All right, so car accelerates from rest for five seconds until it reaches a speed of 20 meters per second. What's the acceleration?

So we're just doing the change in velocity. So we're going from 0 to 20, so the change is 20. So we're just doing that change in velocity divided by the time. So a bullet is dropped from the top of the Empire State Building, while another bullet is fired downward from the same location, neglecting air resistance, the acceleration. They're asking you to make some pretty big assumptions there. So neglecting air resistance.

So air resistance is going to be pretty strong on a bullet after it leaves the gun. So what they're wanting you to think about is that it's not the bullets, the velocity that's important. The acceleration just depends on the gravity.

So regardless of how fast they're moving, they're both going to be accelerating because of gravity. And so our acceleration in both cases is just going to be that 10 meters per second squared. So no matter how fast you're moving, the gravity acceleration is always 10 meters? Nearer surface, yeah.

If you can neglect air resistance, yeah. So as long as you're able to neglect that air resistance, we can say they have the same acceleration. The bullet fired from the gun is going to reach the ground much faster, but its acceleration is going to be the same. So a ball is thrown upwards, neglecting air resistance, what initial upward speed does a ball need to remain in the air for a total time of 10 seconds? Is that total, so it goes from the time it leans and then hits the ground?

Right, so it's going both up and then back down. So if the total time is 10 seconds, that's 5 seconds up and 5 seconds down. All right, and so to stay in the the air 10 seconds, so with that five seconds up, you need to start at 50 meters per second to get the total time of 10. All right, if you started at the 100, you'd be in the air 20 seconds. So 25 compared to a 1 kilogram block of solid iron, a 2 kilogram block of solid iron has twice as much. There's actually all of these.

So the kilogram they tell you, that's the mass, so it definitely has twice as much mass. But because they're both solid iron, the iron has the same density, so they're going to have the same volume. or sorry not the same, the twice as much volume.

And mass and inertia mean basically the same thing. So the more mass you have the more. So with twice as much mass you also have twice as much inertia. And so we're looking for all of these.

An object maintains constant acceleration unless there's a change in... Okay, so the applied force... So that...

Whoa! That's crazy. Okay, uh...

It's gonna be all of them. Yeah, so applied force would do it, but also changing the air resistor mass would also do it. So something just fell off the table?

Okay, uh, yeah I guess leave it on the ground. I'll send in a ticket to support. That's... I guess it's like an electronics cover or something. That's weird.

Alright, 27. Strange as it may seem, it's just as hard to accelerate a car on a level surface on the moon as it is here on Earth. This is because... And so our resistance to change, that difficulty in acceleration, that's the inertia.

And that's the same thing as the mass. And so it's just as hard to accelerate on the moon as the earth because they both have the same mass. No, the car has the same mass on the earth and the moon. All right, now it'd be easier to lift the car on the moon because its weight would be less, but the mass is going to be the same. Eight, a ride on a roller coaster containing six passengers takes three minutes.

Neglecting friction, a similar ride with 12 passengers aboard would take... all right, so we're looking for the same time. Yeah, so the acceleration of the roller coaster doesn't really depend on the number of passengers.

It's still going to go through the same highs and lows at the same speeds, basically. And so it takes the same time. All right, so then a Newton is a unit of force there. So in which case would you have the largest mass of gold if your chunk of gold weighed one Newton on?

So we didn't really talk about the gravity of Jupiter, but Jupiter's gravity is larger than the other two. Does that mean there's more gravity? What?

There's more gravity on Jupiter? Yeah, so at the top of the cloud cover, it's not a solid surface, so you're not standing on something. But the acceleration due to gravity at that point is still higher. OK, so.

We're trying to figure out which has the largest mass, but we say they all have the same weight. All right, so our weight is equal to mass times the gravity. So the one with the largest mass is going to be the one with the smallest gravity.

And so we can say that mass is equal to the weight divided by the gravity. So we know they all have the same weight, and so whichever one has the smallest gravity will give us the largest mass. All right, and so of these, the moon is going to have the smallest, so it would have the largest mass.

All right, so another way to think about that. Because the moon has a small gravity, you need more gold to get up to a weight of one newton. Whereas on Jupiter, because it has a higher gravity, you need much less gold to get to that same weight. All right, so 31 10 kilogram brick and one kilogram book are dropped in a vacuum.

The force of gravity on the 10 kilogram brick is... And so we're looking for the force of gravity. Now if we had asked about the acceleration of gravity, that would have been the same. But when we ask about the force of gravity, that means the weight.

All right, and so the one with the greater mass is going to have a greater weight. Yeah, so, right. And so that term, that force of gravity, means the weight.

And so the weight is the mass times the gravity. They have the same gravity, the same acceleration of gravity, but because they have different masses, they'll have different weight. And so the one with 10 times the mass will have 10 times the force.

In a vacuum, is there still no more gravity, or no? So, a vacuum... Just gets rid of the air resistance. So if an object's mass is decreasing while a constant force is applied to the object, the acceleration... So this goes back to the Newton's second law.

So acceleration is equal to force divided by the mass. So we're saying that the force is constant. But so if the mass is getting smaller, then the acceleration would be increasing.

Sure. So the force stays the same, but we're dividing by a smaller mass. And so when you divide by something smaller, that makes the result bigger. So if we increase the force, that would increase the acceleration.

But if we increase the mass, if we divide by something bigger, that would make our acceleration smaller. So in this case, because we're... decreasing the mass because we're making that bottom term smaller, that actually makes the acceleration bigger.

Alright, 33 10 newton falling object encounters 4 newtons of air resistance. The net force on the object is... And so we're just taking the difference. So the 10 newtons is the weight of the object, and so that's acting down.

As it falls, the 4 N air resistance will be up, and so the net force will just be the difference between those. 34 on the apple weighs 1 N. When held at rest above your head, the net force on the apple is... So we're looking for at rest, and so that's telling us that it's at static equilibrium. And so if we're at static equilibrium, the net force will have to be zero.

What is known as static equilibrium? So there's dynamic equilibrium, where you're moving at a constant velocity, and then the static equilibrium means you're at rest. So heavy block at rest is suspended by a vertical rope. So again, it's starting at rest.

Then when a block is accelerated upward by the rope, what happens to the rope tension? Alright, and so when you're at rest, those two forces will be equal, but in order to accelerate upward, the tension will have to become greater to cause that upward acceleration. Right. So to accelerate upward, the upward force has to be greater than the downward force.

And so the upward acceleration just means that the tension will be increased. So 36, if a non-rotating object has no acceleration, then we can say for certain that it is. Right, and so the no acceleration means that we're at equilibrium, but we have two different types of equilibrium. I guess the mechanical is the...

just the overall term probably better if the mechanical wasn't there all right so we can say for certain that it's at equilibrium But without knowing more, we can't decide whether it's static or dynamic. I set up the... Collaborate to go till 10. I'm not sure if it's going to kick us out.

It's taking a little longer than I expected. So 37, you relax at rest with left foot on one should be a bathroom scale. So you have two bathroom scales. You've got one your left foot on one and the right foot on the other. And so the scales, what can we say about the readings on the scale?

And so we're looking for C there. So they definitely add up to your weight but it's not necessarily equally distributed. Right, so because you're not accelerating up or down, I guess if you were jumping on the scales, if you're relaxed, So if you're at rest, then the net force has to be zero.

All right, so two together have to equal your weight. but it doesn't have to be exactly one half. All right, so tow truck exerts a force of 3,000 newtons on a car accelerating it at 2 meters per second squared.

What is the mass of the car? All right, so we can say our force is mass times acceleration. So we know the force.

And we know the acceleration, and so our mass, we just do the force divided by the acceleration. And then the units are kilograms. So force of 1000 Newton is the acceleration of mass of 1 kilogram at a rate of 1 meter per second squared.

The acceleration of a mass of 2 kilograms acted on by a net force of 2 Newtons is... Okay, so our acceleration is the force divided by the mass. So if we're doubling the force and also doubling the mass, the acceleration will stay the same.

A rocket becomes progressively easier to accelerate as it travels upward from the ground, mainly because... If you don't know anything about rockets, this probably isn't intuitive, but the reason has to do with the fuel. So as you burn the fuel, because fuel has weight, because it has mass...

You're basically keeping the force the same, but if you have less mass, you'll have a greater acceleration. Alright, a jumbo jet has a mass of 100,000 kilograms. The thrust on each of its four engines is 50,000 newtons. What's the jet's acceleration?

meters per second squared. Alright, so acceleration is the force divided by the mass. The force here is not just the 50,000. So that's for one of the engines, but we have four of them.

And then we're dividing by the mass, which is the 100,000. And so we get 200,000 divided by 100,000. And so that's two.

So brakes on a speeding truck are slammed on and it skids to a stop. If the truck were heavily loaded so that it had twice the total mass, the skidding distance would be... So this is probably hard to think about if you've actually tried to slam the brakes on a truck, particularly a semi truck.

So with bigger trucks, it's not as easy as just slamming on the brakes, because if you do that, then the trailer goes a different direction from the truck. But if you just add a single body to the truck, then the heavier load would mean that there's also a greater friction, a greater resistance with the brakes applied. And so if you have those simplifications, even with twice the mass, because there's also twice the force, you'd still have the same accelerations and so your distance would be the same.

So doubling the mass would double the force, and that would lead to the same acceleration and the same distance. Or at least that's how they want you to think about it in that case. All right, so 43, an object released from rest on another planet, requires one second to follow a distance of six meters.

What does the acceleration in meters per second per second do to gravity on this planet? Okay, and so the key there is that this is one second. So in that first second, the distance corresponds to the average velocity.

All right, and so if our average velocity is 6 meters per second, that means that our acceleration is going to be 12 meters per second squared. And so two factors that greatly affect air resistance are... Okay, and so we're actually looking for A there, so it's the size, but then also the speed, how fast it's moving.

Size and mass are the same? No. So the air resistance doesn't depend directly on the weight or the mass.

So the air resistance itself just depends on the how much air you're pushing out of the way, so the size of the object, but then also how much you're changing the speed of the air, so the speed that the object is moving. All right, so when a falling object has reached terminal velocity, its acceleration is... Yeah, so this has to do with the definition for terminal velocity. So that was when the weight was equal to the drag, the acceleration was zero.

Alright, so feather and a coin have equal accelerations when falling in a vacuum because... So we're looking for a d there. It's the ratio of the force, the weight in this case, to mass is the same. So the coin has a greater force acting on it, but because it also has more mass, it still has the same acceleration. All right, 47, an archer shoots an arrow.

Consider the action force to be exerted by the bowstring against the arrow. The reaction to this force is... So this has to do action-reaction.

You have... two forces acting between two objects. So in this case it's the bowstring and the arrow.

And so if we have the bowstring acting against the arrow, the reaction to that is going to be the arrow acting against the bowstring. And so we're just looking for that combination again. So that's D. Skydiver falls towards Earth. Attraction of Earth on the skydiver pulls the diver down.

What is the reaction to this force? So again, it's the Earth acting on the diver. So the Earth pulls the diver down, and so the diver should pull the Earth up. But if we look at the choices, that's not one of the choices, and so it's going to be E. Car traveling at 100 km per hour strikes an unfortunate bug and splatters it.

The force of impact is... So when we have that impact between the car and the bug, it doesn't have the same effect, but it's not because the forces are different. It's because they have different masses.

The force is going to be the same, but because they have much different masses... It doesn't really have any effect on the car, but it has a big effect on the bow. You get different accelerations.

Like in the same direction? It would still splat. So different masses lead to different accelerations. You can think of this like in terms of the Earth and the Moon.

So there's the same force the Earth pulls on the Moon, the same amount that the Moon pulls on the Earth. But again, because they have different masses, the Earth stays... relatively fixed in its position while the the moon goes around the earth.

All right and so another way, so we've got another example, so two people, one twice as massive as the other, tug of war. So there's 12 meters between them when they start pulling on the rope and so eventually they meet and we're trying to figure out how far the heavier person slides. And so in terms of their mass, they're going to have different accelerations. So the lighter person is going to move twice as far as the heavier person. All right, so if we think of the the distance that the heavy person moves as x, Then the distance the light person moves is going to be 2x.

And so our total is 3x. And so that equals the distance to 12 meters. and so the distance that the heavy person moves is just 4 meters. Alright, so that's all we're doing for lecture today. If you have any questions, feel free to email.

Transcript for:Physics Class Exposure and Lab Guidelines

Transcript for:
Physics Class Exposure and Lab Guidelines