Hello everyone, welcome to Magnet Brains. I am Avneet Kaur and today we will study the chapter of Class 8 Science, Friction. So what is friction?
If you roll down a ball from a slope, it stops after rolling down easily. It doesn't happen that the ball keeps on moving and never stops. Similarly, if I am cycling, then if I roll down the ball, it stops after rolling down. If I stop paddling, then it won't happen that the cycle will keep on going. So there is something that is opposing the motion and that is friction.
Like you must have done this childish mischief that you threw a banana peel and someone fell because of it. So can you tell us why this happened? To know the reason for this, first we have to know why we are able to walk on the ground. Because our feet and our ground there is a force of friction between them if I push the ground in the direction of backward then the ground pushes me forward and this is possible because of force of friction which is acting but if banana peel What will happen if the banana peel comes on the way?
The force of friction due to which I am able to walk, this force will reduce. If it reduces, I will not be able to walk, I will slip. So whenever we throw banana peel, what are we doing?
Rough surface, that is, our road or ground, we are converting it into a smooth surface. And as soon as the surface is converted into smooth, the friction will decrease. Due to which we will not be able to walk, but we will slip. So I hope you understood the basic idea of friction. So let's see more examples.
It is difficult to walk on smooth and wet floor. Yes, if I drop water on the floor, will you be able to walk? No, you will slip. Why?
Because friction reduces on wet floor. And friction reduces because smoothness increases. Because of which we slip.
But we have to remember one thing always. friction and motion direction is opposite to each other. So, let's see through an example. Suppose if I talk about a ball's motion, then this ball is moving here because I pushed this ball from here.
So, if I kick this football from here, then it will move forward. But, it will be on the ground. So, the force applied on the ground in the opposite direction, we call it frictional force.
So, frictional force is applied in this direction. So this is the direction of motion because it is moving and we have applied force but friction will act in opposite direction. That is why the ball will not be moving continuously, it will stop at some point.
Because when friction increases, the ball will not be able to move further, it will have to stop. So that is why friction always opposes the applied force. The force of friction is the force of motion. friction Q oppose cut that QQ's direction he opposite hotel motion K directions so I hope you have to so much may argue up from spring balance K bar me putting it to spring balance Jessica I've a big sick take device it just make a boat sorry calibration sub deck sector to suppose many spring balance K who pick way object put here object kya karega?
Ye object jo hai wo spring balance ke spring ko pull karega aur kitna pull karega? Jitna uska mass hai uss asaab se pull karega. To spring balance hume force ka measurement deta hai. So spring balance is used for measuring the force acting on an object. So, the force is measured.
How? Because there is a spring attached here and as soon as I attach the object, the object will pull it. Because of which, we get to know the value of force according to the mass of the object. So pointer moving on a graduated scale you can see over here in this diagram this is the pointer it will move over the scale why what do they mean by a graduated scale graduated means this up the scale of the will be graduated with a zero say once centimeter k beach map key 10 lines with the end then 0 to 1 then 1 to 2 and so on so this is known as a graduated scale so I hope this is clear of your spring balance me napo cube at a Yuki may is related activity carnival you listen many kaki many spring balance me make suppose make a specific break I have put the weight of the brick here.
And then I am seeing that the spring balance is being pulled down because of the weight of the brick. And here I will get the measurement of the force. Now if you tie a polythene around a brick and then carry it, what do you think? Here frictional force will change because polythene is will smoothen the surface friction force will be reduced so your reading will automatically change on your spring balance so this is how we study with this with the help of the spring balance how does the value of frictional force changes so I hope this is clear to you that it gives you the measure of the force of friction between the surface and the brick so I hope this is clear ok so now we will see how friction occurs this is a wood block and I have placed another object on it it is difficult for me to move this object why is it becoming difficult? Because the force of friction is acting between which two?
Between this object and this surface the force of friction is acting So what is this friction? What happens due to friction? Due to friction, these two surfaces interlock. As I told you that there is a lock and a key, so the key fits perfectly in the lock.
Similarly, the two surfaces between which the frictional force acts, one surface's irregularities get locked in the irregularities of the other surface. That's why motion becomes difficult. So this is how friction plays its So, the irregularities on the surface will increase the friction force. The more irregularity, the more force of friction because interlocking is more. So, when will the force of friction increase?
When the surface will be rough or smooth? We just saw why we slip on an apple peel. Because friction decreases.
Because the surface becomes smooth. Meaning, rough surface may force of friction zyada hoga or smooth surface may force of friction kam hoga. So I hope this is clear. Toh kuch na kuch agar suppose main baat karu ek object hai and usko uska motion start kar rahi ho. Toh main ek ball diya aur usko dhaka mara.
Toh abhi bhi kuch na kuch force of friction aayega play mein. Aur agar main ek moving object ki baat karu toh moving object ke motion mein bhi friction role play karta hai. For example agar main baat karu agar aap bicycle ride So, as you are riding a bicycle, you have to put some effort because if the air is in the opposite direction, you will get a lot of friction due to the air. Apart from that, friction will also be there between the tyre and floor of your cycle. So, to overcome that friction force, you have to put a lot of effort in riding the cycle.
So, if we talk about force required. to keep an object moving with the same speed is known as sliding friction. So, if an object is not in motion but on rest, now I have to start its motion. So, there will be some opposing force which will not allow its motion to happen.
So, this opposing friction force is called static friction. Static means stationary. is static friction. But if an object is moving, like we took the example of a moving bicycle, then in the case of a moving bicycle, the motion that has started and the friction that is still applied, we call that friction as sliding friction. So can you tell me if static friction is more or sliding friction?
Yes, static friction is more because the object has to bring motion from rest. Sliding friction acts when the object is already in motion. So, you can see that your shoes have grooves in them. That means they are not smooth. They have some irregularities.
Can you understand why this happens? And if I talk about it, if you keep using shoes for a while, they become like this, completely smooth. And if you wear such shoes, then the chances of falling are also high.
So, now do you understand why there are grooves in shoes? And when the grooves become flat, why does the motion become difficult? Yes, the answer to this is friction.
So, we can walk because the ground and our feet are in the same position. between which friction force acts. If this friction force is not there then we will not be able to move. And the grooves in the shoes increase this friction so that we can easily walk.
But if these grooves become flat then what will happen? The surface becomes smooth, friction will decrease and we will slip. So therefore it is difficult to move on a wet muddy track or a marble floor. Again marble floor is a smooth surface.
You will not be able to walk on it. Because friction will be very less. If an object is started moving, it would never stop if there were no... friction just like we have taken the example of ball that it will keep moving but this does not happen because friction force acts opposite to the direction of motion of the ball. So I hope this is clear to all of you.
How is friction a necessary evil? Now next you must have read that whenever machines work, there is a lot of heat release. Like suppose you go to an iron and steel manufacturing plant, then you know that the parts of the machine move against each other and due to this motion friction comes and this motion and friction force opposes it. heat release. That's why you must have heard from someone that always do greasing in machine parts.
They work smoothly with greasing. Why? Because by doing greasing, we increased smoothness and reduced friction. So machine parts won't rub against each other and heat release won't be so much and machine parts won't spoil too. So I hope this is clear to you.
Again, This is a very common example. You must have seen that whenever you feel cold, you can rub your hands against each other. Due to this motion, the friction force that will oppose this motion will produce heat and your hands will feel less cold.
You will feel better in a very cold environment. I hope you have understood how friction is useful and how it can be useful for us. Because if we talk about machines, then machines release a lot of heat and the parts of the machine get damaged.
Why? Because of friction. So I hope this is clear to you. So for the complete course, you should definitely upgrade to Magnet Brains Plus.
We have kept its price quite nominal. Till then, in our next video, we will study more about friction. Thank you. Hello everyone. Welcome to Magnet Brains.
I am Avneet Kaur and today we will study about friction. Friction. This class is about the topic of Age Science.
In the last class we had studied why friction is important and in some cases when friction behaves like an evil. So basically in today's class we will study the methods by which we can increase and decrease friction according to our needs. So you must have seen that your shoes or footwear have such grooves that they are not regular smooth or flat.
surface is a little uneven. Do you know why this happens? So that it can provide friction and you can move on the ground easily. If it was flat, that is, if I take an example of an old shoe, that is, suppose it falls, which is flat, then there are more chances of falling because friction reduces as soon as the smoothness of the surface increases. So if friction reduces, then what will you do?
You can fall on the ground. That is why grooves in your shoes. Again, the tires of your vehicles are very smooth surface tires that you must have seen small spikes in them.
Like here, so we call this treading. So why do we need treaded tires? So that friction can come between the tire and the ground so that the car can move forward and not slip.
So that is why the treading is important. tires are treaded to avoid slipping and to increase friction. Again, if we talk about when you are riding a bicycle, there are brake pads in it, so they also have a similar function. Then Kabaddi players, what do kabaddi players do? They rub their hands with the ground.
The sweat in their hands is It increases the smoothness of the hands which means it reduces friction If they touch the ground, their hands will become rough and they will be able to easily snatch their opponent and their hands will not slip So to avoid slipping, they have to increase the friction due to which they rub their hands in the soil So I hope these examples are clear to you Now if we talk about next, we will talk about reducing friction. So when will it happen that we need to reduce friction? Yes, our favorite game, carom. So we spray a powder in carom, sprinkle it.
so that the balls can slide easily to make the surface smooth we have to reduce friction for this we have to spray powder powder, what is the chemical in it? That is boric acid. So, because of this, smoothness increases. So, I hope this is clear to you.
Now, we apply grease in the machines so that the parts of the machine which are rubbing with each other, they do not get spoiled. Friction is minimized. So, to increase its smoothness, what do we apply? Lubricant.
And grease is an example of lubricant. So, friends, what is lubricant? A substance that reduces friction. So this is the action of lubricant, it reduces the friction. So I hope this is clear to you.
One more example that you must have seen in your day to day life. Sometimes the doors start making noise. So what we do is we put some oil in their sides. What will the oil do?
Oil will lubricate. And what happens? because of lubrication, the sound will stop.
So, a few drops of oil are put on the hinges of the door. So, this is again done to smoothen the surface to minimize friction. Okay, now we'll do another activity. So, till now we had studied two types of friction, static and sliding friction. But, what we will study today is the third type of friction.
So, you imagine that... If you place a wood block on top of 3-4 pencils, will the motion of the wood block become easier? Yes. And this friction is minimized because the friction in the roll is not there.
in play is what friction? Rolling friction as you can see here I have applied force here so friction will act in opposite direction but the friction that will act is rolling friction because this block is rolling on these wheels so which friction will come in play? Rolling friction So, I hope this is clear to you that pencils roll and resistance to the motion is reduced.
That means, can I say that the value of rolling friction is very low. Yes, that is why rolling is very easy as compared to sliding. So, you must have seen that in luggage carrying bags, there are balls and wheels.
What do they do? They reduce friction. and you can easily attach or carry your bag. So why do we use this? So that we don't have to work hard to move our suitcase.
So that is why we put below it some circular wheels and we make the use of rolling friction which has minimum value so that we don't have to put much effort to pull our suitcase. So do you agree that rolling friction is the least in value and more than rolling friction sliding friction and the most valuable is static friction because we have already read that the value of static friction is more than the value of sliding friction so I hope this is clear to you so rolling reduces friction this is the reason and this is the summary sliding is replaced by rolling by the use of ball bearing so here you can see the ball means the spherical wheels or ball bearings like I will show you an example I will show you a picture of the earrings so that you can understand. So here is the ball bearing. Now if you see the surface of the ball bearing, this is a very smooth surface.
And due to this smooth surface, friction will reduce. And because it is spherical, which friction will come into play? Rolling friction. So now let's move to fluid friction.
So of course, we should know what is fluid first. So let me tell you what fluid is. Both are fluids.
Solids are rigid. So, liquids and gases are fluids. So, do they also offer resistance to motion?
Do they also require friction? Yes, and that friction is called fluid friction. So, air, water, all these exert friction.
We know that if we are riding a bicycle and the air is going in the opposite direction, then our air is going in the opposite direction. speed come ho jati hai due to fluid friction. So, frictional force exerted by fluids is also called fluid friction or a drag.
Now, agar hum baat kare ki frictional force kis kis factors pe depend karta hai fluids ke case mein, speed of the object, shape of the object and nature of the fluid. To aayi hai in sab objects ko, in sab parameters ko hum detail me study karte. So, you tell me, if I tell you that your speed will be more, then will the friction force be less or more? If you will ride the cycle very fast, then you will easily overcome the friction force and you will be able to move. So, the more speed you have, the more you will be able to move.
Next, let's talk about shape. You know that birds have streamlined bodies. Fishes have streamlined bodies. So why is the body of fish streamlined? Because fish have to stay in water and water is a fluid and fluid friction act in it.
When fish move, the fluid in which it moves will apply friction force and to overcome that frictional force only the body of the fish is streamlined. Similarly, birds fly in the air so their body is designed in such a way that it opposes the frictional force of air. If I tell you that imagine a bird flying and an aeroplane flying. So you will see there is a slight similarity in the shape. Both have wings.
So why is it so? Why have we designed the aeroplane in such a way? So as to minimize the fluid friction caused due to air.
Aeroplane is flying in such a way and due to air, the air is getting more and more fluid. force is like this, to minimize it, this shape is given. So I hope this is clear to you.
Again, vehicles are designed in such a way that their shape is such that they can reduce friction and their motion becomes easy. So I hope you have understood this. So this completes your chapter and now in our next video, we will discuss the NCRT solutions of this chapter. For the complete course, definitely upgrade to MagnetBrains Plus which we have made available at a very nominal price. Till then, thank you.
Hello everyone, welcome to MagnetBrains. Today we will study about friction. This is the topic of class 8 science and today we will discuss its NCRT solutions. For the NCRT solution, we will discuss the NCRT solutions. question fill in the blanks friction opposes the dash between the surfaces in contact with each other friction motion co oppose karta hai toh ishele aapka answer ho gaya motion friction depends on the dash of surfaces smooth surface hota hai to friction come hota hai rough surface hota hai to friction zyada hota hai nature of surface friction produces dash so we pata hai machines In this case friction reduces heat and that is why friction is even.
Sprinkling of powder on the carrom board, if we spread powder on the carrom board, it becomes smooth and the friction decreases. So it decreases or reduces friction. Sliding friction is dashed than static friction. So we know that sliding friction is during motion and it is definitely less.
That is why less than the static friction, just stationary. uh So, the next question is, four children were asked to arrange forces of rolling, static and sliding friction. So, we have already read that rolling friction allows the easiest movement. So, it is the least active.
sliding friction is slightly more than that and static friction is even more. So the answer would be C static sliding and rolling. I hope this is clear. We have discussed this in our video lecture.
we were discussing this chapter. Question 3. Alida runs her toy car on a dry marble floor, wet marble floor, newspaper and towel spread on the floor. The force of friction acting on a car is different but what is the increasing order of this force?
What will be the lowest friction force on a smooth surface like wet marble floor? And then on dry marble floor because there is no water, the friction will increase a little. And if we talk about newspaper and tile, newspaper is rough and tile is even more rough.
So friction on tile will be high and less on wet marble. So has the increasing order of friction happened? Yes.
Suppose your writing desk is tilted a little, a book is kept sliding down. Show the direction of friction force. So, we have studied that friction opposes motion. So, if the book is going down, the direction of friction is opposite. motion of book is below then friends friction will oppose it by going that way so direction of friction force would be opposite so I hope you have understood this sliding has been shown as per the question You spill a bucket of soapy water on marble floor accidentally.
Would it be easier or difficult to walk? Soapy water gir gaya. Aap soapy water ke girne se kya hoga?
Aap slip karenge, ye toh aapko pata hi hai. Aap slip kyu kat? We all know that we can walk because there is friction between our feet and the ground.
So we push the floor backward with our feet and we can move forward. So if this friction... force come ho jaye toh kya hum move kar payenge? Nahi. Aur soapy water friction force ko kam kar deta hai, surface ko smooth bana deta hai, isi liye we tend to slip.
So the answer is no. Kyun? Kyunki it will be more difficult to walk because friction is decreased or reduced. Explain why sportsmen use shoes with spikes. So we know that if shoes have spikes, then friction will increase and it will make them easier to move.
Whereas if I use smooth or flat surface, flat shoes, in which there are no spikes or grooves so what will happen is that friction will be reduced and I can slip while walking so I hope this is clear Iqbal has to push a lighter box on sema has to push a similar heavier box on the same floor who will have to apply a larger force? So if I talk about heavier box and lighter box, surface is same but heavy box's weight due to which interlocking between the two surfaces will increase. That means frictional force will increase and in light case the interlocking of surfaces will decrease because it is light in weight.
it will be easy to move the right one because in that case friction will act less. So I hope interlocking of surfaces is clear to you. Explain why sliding friction is less than static friction.
Sliding friction is applied when a body is moving and static friction is applied when you are resting. So in static friction we give more time. Explain. For example, I have placed a body. Now what happened?
Interlocking between surfaces happened. And for this, we got more time because the body is on rest. But if a body is moving there, then for interlocking of surface, we don't get time because the body is in motion. So, that's why static friction would be greater than sliding friction. Give examples to show that friction is both a friend and foe.
We know that we are able to walk because there is friction. Between our feet and ground, we are able to write because there is friction. between the paper and the pen or pencil tip with which we are writing. Again disadvantages of friction are that the soles of our shoes get scratched, the tires get damaged after some time and we know that the parts of the machine rub against each other and get damaged due to frictional force. They also release a lot of heat.
So this is how friction is an evil. Explain why objects are moving in fluids must have special shapes. So we know that if fish has to move in water, then water which is a fluid, which offers fluid friction, drag bhi bolte hai usse oppose karna hoga.
Toh isi liye uski body streamlined hoti hai uss tarike se. Similarly jo birds hai unko air ki wajah se friction ko overcome karna hoga. Toh unki body designed hoti hai uss tarike se ki wo uss friction ko overcome karna overcome kar ke move kar paye.
So I hope this is clear to you. So this completes the NCRT solutions of this chapter. To complete course ke liye magnet brains plus mei zarur upgrade kare.
Humne iska price kaafi nominal rakha hai. Thank you.