Let's move on to the next chapter which is Gravitation. Let's do it quickly. It's a very simple chapter. Gravitation and Sound. It's a very simple chapter.
Now, do you know what I feel? I am afraid that this mic might get dised again. I am thinking that I don't have any other mic with me.
Which I can use today. Otherwise, today I will be with you. Otherwise, I will be with you. I will be with you. You will say, bro.
I am not going to do it again. So, what is gravitation? First of all, we have to start with what is the universal law of gravitation? Law of gravitation says that whenever two bodies are present they will apply force to each other. That force will be directly proportional to the product of masses and inversely proportional to the square of the distance between them.
So, what is our final result? F equals to G M1 M2 by R square. In which G is Universal Gravitational Constant.
Everyone knows this. Universal Gravitational Constant. Remember its value. 6.67 into 10 raised to the power minus 11. Don't forget.
It's important. You should remember this. They don't give this value in the paper.
Come. So this is Universal Law of Gravitation. Now here comes a very important derivation.
Acceleration due to gravity. That is small g. How will we find that?
Its derivation is important. Understand this is very important. There is a formula, force equals to mass into acceleration.
Do you know? Do you know? Very good.
And what is the force here? Force is equal to G m1 m2 by r square. And this will be equal to mass into acceleration. That is m1 into acceleration.
That means you can cut the second m from one m. So the acceleration, that is Acceleration due to gravity will be equals to gm2 by r square. gm2 by r square. Means, if I want to find acceleration due to gravity of earth, then what will I do? Formula has come.
gm by r square, in which g is constant. What is m? m is mass of earth. That too is constant. And what is r square?
Radius of earth. That too is constant. So, we will put all these values. and the value of g is 9.8 mpsq. When we calculate, it is 9.8 mpsq.
Or we can write 10 mpsq. How does small g change? Like it changed color in your life, it also changes. Remember how it changes, how variations occur.
First, if you increase the height, suppose you are going very high, Then your small g will decrease. Remember, small g always decreases when you increase the height. Similarly, if you increase the depth, even then your small g decreases.
If you increase the depth, even then your small g decreases. And the next thing is latitude. Try to understand what latitude means.
I will explain you how your earth looks. This is your earth. This is your Earth.
What are these? These are your poles. And here is your equator. It is of this shape.
Now see, which distance is smaller? Which distance is smaller? Tell me quickly.
Which distance is smaller? Tell me quickly. Earth is not round.
Which distance is smaller? Wow! Wow! Hey kid!
We are still writing pole, not pole but equator. It is obvious that the distance of pole is small. Remember the formula. g m by r squared. The distance of which is less, won't its g be more?
That means, the acceleration due to gravity here will be more and the acceleration due to gravity here will be less. Can I write here that pole pay acceleration due to gravity is greater than the acceleration due to gravity in equator. Done, beta. Very good.
Very good. Very good. Done?
Done? Right. Clear.
Absolutely. Let's go. What is the difference between small g and big G? Small g changes. It changes its color.
Small g's value is changing, right? Again and again. But big G is a universal constant.
Its value will always remain the same. It doesn't change. It is like your friend.
It is like your ex. Okay. Okay. What is the difference between mass and weight?
Mass is constant. My mass will always be constant. Weight is equal to mass into acceleration due to gravity.
You calculate your weight. Your mass is the same as 70 kg or 80 kg. Weight is always counted in Newton.
Weight is mass into acceleration due to gravity. Suppose you go to the moon from here. Go to the moon. Suppose you go to the moon from here. Your mass will be same on the moon.
Which is 70 kg. But your weight will change. Why?
Because acceleration due to gravity on the moon will be different. Okay. So remember.
What is mass and weight? Mass will always be scalar quantity. Weight will always be vector quantity.
Why? Because weight will change. Yes. Weight will change on the moon. This unit is not changed, it is changed.
Its unit is kg and its unit is Newton. Okay. Next concept is thrust. What is thrust?
Thrust is basically force acting on an object. Thrust is nothing but force. Whenever a perpendicular force is applied, we give it a name other than force, thrust. So perpendicular force is called thrust. Nothing else.
The unit of thrust is also same. The unit I am telling you is Newton. Let's do a question of gravitation.
Whenever we drop something or throw it up. I am telling you a trick. Whenever you drop something from above. You are dropping it with gravity.
I am telling you a trick. It is done in every sub-school. Whenever something falls.
So always take G as positive G will always be positive Acceleration will always be positive Why? Because it is coming in G direction Gravity is also going down And whenever something goes up Always take G as negative Remember this much Rest of the formulas will be same The formula we were reading B equals to U plus AT There G will be converted in one place Why? Because we are throwing things from top to bottom Okay now see If you do this, you will understand. A ball of mass 2 kg is dropped from a height 20 m. We have dropped something from 20 m.
Suppose this is a ball and it was 20 m. I have dropped it. Now find the time taken by the ball to reach the ground. How much time will it take? Tell me, how much time will it take?
What will be the initial velocity? Will it be 0? Will the velocity be 0 while dropping?
I want to find the time. How will I find it? Which formula should I use?
Don't do this. If you are given this, then you can use the formula s equals to ut plus half at square. But in this condition, it will come to g at the same place. Because it is gravity in acceleration.
So the formula will be s equals to ut plus half gt square. Now u is 0, so the whole term will be 0. So what will be your? S equals to, how much is the value of S?
20 meters. So write here, 20 equals to half into gravity's value, let's assume 10. Let's take 10 and positive 10 because it is coming down from above. And what is T square? Time is to be taken out.
Time is to be taken out. So send it here. So this will come, the value of T square will come, your 4. And the value of T will come, your 2. So time came 2 seconds.
Whose 2 seconds came? Whose 2 seconds came? Tell me quickly.
2 seconds for each. So, the time that you have taken is 2 seconds. Now, it is the same thing. Calculate the velocity with which the ball will hit the ground. At what velocity will the ball go?
What will be the final velocity? How will you find it? V equals to U plus 80. U is 0. Acceleration is 10. Time is 2. So, it will be 20 meters per second.
Wow, brother. Look at the next. find the force at How much force is there on the ball?
How will I take it out? Is the ball mass given? Is the acceleration given?
10 mps is given. So tell me quickly, how much is the force? Force is mass into acceleration.
That's it. Simple acceleration into gravity is 10. Next. If the ball rebounds with the same velocity, what is the impulse?
Let the question of impulse be. Because impulse is out of the syllabus of NCRT. Some schools do it.
But logically, it is out of NCRT. Impulse is nothing. Force into time is impulse Impulse is force into time But yes, this is out Which law of the motion explains the rebounding? Because of which the rebound happens? If something goes down And that thing goes up Why did it come?
Tell me Why did it come? Every action has an equal and opposite reaction Very good Very good Okay, every action has an equal and opposite reaction Is everyone here? Come on Done?
Done? Very good Now let's talk about pressure Pressure is thrust by area. It is force by area.
Pressure is thrust acting per unit area. Its unit is Pascal. Don't make B as R or your parents will beat you. This is Pascal.
Pascal is unit of pressure. Pressure is force by area. If area increases, then pressure will decrease. Absolutely.
Right? And here we are asked some questions. Why does sharp knife cut better? Why can you cut better than sharp knife?
Because sharp knife has less area. If area is less, then pressure will be more. Similarly, why does the camel have broad feet?
Camel has more area of feet. If area is more, then pressure will be less and it will be able to walk properly. So, such logical questions are coming in your paper. Next concept is bio-end force. What is bio-end force?
Whenever you put something in water, So water puts an upward force on it. We call it as biont force. Upward force exerted by a fluid. If you put anything in water, it will come up. Now, there is a concept here.
Law of flotation. What does law of flotation say? Law of flotation says that it is a game of density.
Suppose there is water and an object is put in it. If the density of water is more in comparison to the object, then it will float. If the density of the object is more than the density of the water, then it will sink.
And if the density of both the objects is equal, then it will stay above the density of the water. Remember, the body will float in a liquid if its density is less than. If it is less than the water, then it will float.
If it is more than the water, then it will sink. This is the simple law of flotation. Floating, sinking, suspended.
Now, the next thing that will come in your paper is the define Archimedes principle. Archimedes principle, what is it? Try to understand. Archimedes principle says that when an object is immersed in a fluid, experience an upward buoyant force equal to the weight of the displaced fluid. That means, let's say you put anything in the water, the buoyant force will be equal to the weight of the displaced fluid.
That means, what is he saying? the The force on an object will be equal to the weight of water displaced. Weight of water displaced. The amount of water that object has released. Did you understand?
Do you remember the statement? Tell me quickly. Do you remember the statement? This question is asked a lot of times. I was asking you a lot of times.
A lot of times. Okay, let's go. Now, this is a little...
I want to tell you a main part of this question. See this C part. If a person weighs 60 kg on earth, what will be their weight on the moon? You know that the acceleration due to gravity on the moon is 1 by 6 times. Now tell me if a person has a 60 kg mass So, what will be its weight?
This is mass in kg. This is not weight, this is mass. This is mass. Yes, very good. Very good.
Means, what will happen? Weight will be M into G. And what is G here? G by 6. So, 60 into 10 by 6. So, this will be your what?
100 Newton. 100 Newton will happen, fools. 100 Newton. 100 Newton will happen, son.
Which one are you doing? Which one are you doing? I was writing 10 Son I was writing 10. Will you get beaten up?
Will you get beaten up? Will you get beaten up? Will you get beaten up?
Will you get beaten up? Will you get beaten up? Did you understand? Let's go. This is your chapter.
This is your gravitation. Now comes your work and energy. Then comes your last sound chapter. Come on, brother. How long is the class?
It's another half an hour class. Son, please read it. Please. My mic is going to get dis-ed. My mic is going to get dis-ed.
Son, my mic is with me with a lot of sorrow. I am going to get dis-ed. My mic is going to get dosed.
My mic is with me in a lot of pain. Very sad. Huh?
Come on. Hey, how are you writing 10? You tell me one thing in that question.
Tell me one thing. Tell me one thing. Here, this weight is not given.
This mass is given. Mass. What is weight?
Mass into acceleration. Dude, what are you talking?