we are back and we are still in section 3.3 still talking about energy transformations and the idea of transforming energy from one form to another is the basis of this is kind of a classic science fair kind of project and what you're seeing here is using a lemon battery so using a lemon and notice that you've got these two screws stuck into the lemon and attached by a wire to what a little electric motor and basically the ele the lemon with the two metallic the screws stuck in that's going to be chemical energy converting into electrical energy that's a battery and that lemon and the metals that that initiates a chemical reaction and that releases energy and then we use that energy to power the little electrical motor and what's inside that motor yeah we don't know yet do we we will find out we will learn how those motors work when we get to the chapter on electricity and magnetism but energy then electrical energy being transformed into this mechanical energy it's going to spin that fan and that fan is going to propel the car forward so again lots of energy transformations to be thinking about we can convert these forms of energy back and forth and what we notice is that there aren't any prohibited conversions we can go from electrical to radiant energy we can go chemical to mechanical we can do these transformations in any combination however the one thing that and we're not ready yet to go into detail but the one thing that we notice whenever there is an energy exchange there's always waste heat there's always heat and we'll need to figure that out a little bit later why the process of energy transformation always generates waste heat but you're you already know you already know that that happens you turn on a light and the light bulb gets hot you eat breakfast and you walk across campus that chemical energy converted to mechanical energy as you walk across campus you're also going to generate waste heat you get warm you get in your car and drive the engine gets hot it's not just chemical energy straight to mechanical energy car goes down the road there's also waste heat generated so every example that you can think of creates some kind of waste heat but energy is conserved and what we mean when we say that energy is conserved is exactly what we meant when we said momentum was conserved exactly what we meant when we talked about momentum excuse me we recognized that you could redistribute that you could take momentum from one object give it to another object and the individual pieces of our system could change but the overall momentum of the system stayed constant and that is exactly how all conservation laws work so conservation of energy works the same way the energy can be moved from one object to another the energy can be transformed from one kind of energy to another kind of energy but you're not going to gain or lose your total amount is going to stay constant the books are going to balance it is just like accounting the books are going to balance and excuse me if you think that you're seeing a violation of energy conservation all that's telling you is look harder the energy you think is gone is somewhere it's somewhere but maybe you're not looking for it in the right place or maybe it's not the form of energy that you were anticipating so what is this device that we're looking at um the picture this is what is called a ballistic pendulum and this is a really classic example of energy transformations and energy conservation and also collisions and momentum conservation this little device is is a really compact lesson in a lot of different physics but what i want to point out here is the idea of transforming the energy now what you cannot see you can see right at the tip of this gray cylinder there is that's a stainless steel ball and the handle at the other end here well it's like when you play pinball how you pull the handle to compress a spring and when you let go the spring releases and launches the ball it's just like that it's exactly like pinball you just can't see the spring because it's encased in the the metal housing so the first step is compress the spring so you are going to do work you're going to have to pull the lever do work to compress the spring you're storing energy in the spring now when you release the spring the spring potential energy is transformed and where is that spring potential going to go it's going to be used to launch that ball so we're going to transfer that spring potential energy the elastic potential turn it into kinetic energy of the ball and then that kinetic energy the next thing that happens the ball is going to run into this block and that block is a lightweight plastic block and it's got a little bit of a hole board into it so that the stainless steel ball is going to hit and it's going to just stick it's going to stay they're going to stick together we've seen that kind of collision before that was the kind of collision that that you looked at in lab number four so there's your momentum conservation and now so we've had an energy conservation an energy transformation and now we've got a momentum conservation where the collision happens between the ball and the block and now that block it's on strings here so that block is free to swing now that block has kinetic energy because the ball just gave it some kinetic energy and it's going to swing and you see there's a protractor there that's the thing that we would be measuring but that block is now a pendulum and it's going to swing how far out depends on how much energy it has because that is now your last energy conversion the block has excuse me kinetic energy that swings up kinetic converts to gravitational potential energy and so where does the energy go we can follow step by step by step by step and then we ask the question where does energy go that we don't take into account because the book's balance so i also use this example because there's several places where energy is transferred or transformed that you can't measure and so when you perform the experiment well it looks like you're not conserving anything but then you want to think about why so just a couple of examples here at the very first step when you compress the spring and then you release it all of the spring energy we assume that energy is going to go to that stainless steel ball some of it gets lost it's not really lost but it's just not given to the ball it's dissipated in the form of sound there's a loud sound that happens and that's a form of energy so i'm sorry so we are going to have right there one example of where energy goes if you think the energy is gone look harder okay there's one really good candidate there's where some of the energy went another good candidate is if you see right on the edge there's this red thing at the edge of the white block and that is not attached to the block it's attached separately from the block and when the ball hits the block and becomes embedded that block moving forward is going to hit that pointer because that's what that is it's just a pointer so that the block is going to push that pointer forward and it's going to show you the angle but what just happened there well we just had another collision and another place where some energy went that we didn't account for so my whole point in looking at this slide is to get us into that kind of mindset where we have to be sure that we're looking at everything that matters at everything that is involved in what our system is when we did collisions we were really careful and said what's only this object and this object these are the only two things that we're going to look at and for our analysis of collisions at the level that we were doing it just basic getting used to it that works perfectly that works just fine but now that we're seeing this idea of energy transformation this is a lot more complicated there's a lot of different kinds of energy i mean momentum is momentum there's only one kind of momentum object in motion and so now it becomes a more complex problem automatically because there's places for energy to be exchanged and for energy to be dissipated that don't exist for momentum okay one more slide and we're done with the section very last idea and we are just bringing this up and we can't answer the question yet we keep talking about the spring gives energy to the ball this gives energy to that energy is transferred from object a to object b and we have not answered the question how does that energy get transferred exactly how does that energy get transferred and it's a question that we can't answer because it depends on the kind of energy that you are trying to move and what are objects a and b that you're trying to move energy from and give energy to so we're looking at a pan on a campfire here for a reason because right there we are seeing multiple mechanisms of energy transfer right there and we're not quite ready to explain them but when we get to the chapter on heat when we start talking about heat then we'll be ready to start explaining how energy is actually transferred from object to object we are done with this section and when we come back we'll be starting section number four 3.4