Hi friends, did you know that when I move from there to here, I just disturbed the entire universe. By disturb, I mean a force, which is a push or a pull in physics. So when I moved from there to here, I disturbed everything in the room around me.
I've even disturbed you, wherever you are on this earth, and the moon, the sun, the stars, everything. It sounds unbelievable. right?
But it's true. Stay tuned because you're going to learn more about this on this video on gravitation. And then we'll finish off with our top three exam oriented questions on this topic.
Let's start with the basics. When I drop this ball, why does it fall down? It's because earth is pulling it down with this invisible force called gravity. In fact, the the earth pulls all the objects.
That's how I am standing on the ground or you are sitting. We know that the earth pulls the moon, the sun pulls the earth and all the other planets with this invisible force. But the interesting question is, do all bodies pull each other with this invisible force?
For example, am I pulling this ball right now? Or are you pulling all the things around you? It may seem strange, but the answer is yes. And this invisible force is called the gravitational force, which we are going to analyze.
As we learned, everything in the universe is pulling everything with this gravitational force. What's the requirement? The body should have mass. the gravitational force is always attractive.
So for example, these two blocks that I have on the table here are attracting each other with a gravitational force. Let's take a look what this force depends on. Force is directly proportional to the masses.
What does this statement mean? So let's say the force between these two blocks is 1 Newton. Now if I double this mass, so I am going to add another block here.
So what's going to be the new force between the blocks? That's right, it's going to get doubled. So the force will be 2 Newton. Now let's say we triple this mass. So here we have 3 times of the original mass.
Now what is the new force between the blocks? It's going to be 6 times of the original force. So the force will be 6 Newton. So the gravitational force is directly proportional to the product of the masses. Force is inversely proportional to the square of the distance between the two bodies.
What does this mean? So we saw that the force between these two bodies was 6 Newton. Now let's say I double the distance between the two bodies. So what will be the new force now? It's going to be 1 fourth of the original force.
So that's 1 fourth of 6 Newton which is 1.5 Newton. Now let's get these blocks to their original position. Now let's say I halve the distance. So when I bring them in, so what will be the new force now?
It's going to be 4 times the original force because it's the square of the distance. So the new force is going to be 24 Newton. And this is called the inverse square law. If we combine the relations, gravitational force is directly proportional to m1, m2 by r squared. Where m1 is the mass of the first body, m2 is the mass of the second body, and r is the distance of separation between the center of masses of the two bodies.
mass or the distance of separation between the two body changes then the force will also change and that's exactly why i said in the beginning of the video that when i moved from here to here the distance between me and all the objects inside the universe changes so the force will naturally change and that's how I disturb the entire universe when I move from there to here. To convert the proportionality relation into an equation, we need to introduce a constant of proportionality. It has the symbol capital G.
So our equation becomes F equal to g m1 m2 by r square, where g is called the universal gravitational constant. Now what's special about it? g has the same value in the entire universe, no matter which two bodies you're considering.
The value of g will be the same. The scientist measured the value of g. It's really really small. 6.67 into 10 to the power minus 11. Now what are the units of g?
Well, there's no need for you to remember it. You can easily derive it from the formula we just did. So if you rearrange the formula, we get g equal to fr squared by m1 m2. So what will the units of g be? Newton meter squared by kg squared.
Now let's get a feel of the value of g with the help of a simple example. If we take these two books, each having a mass of 1 kg. And let's say they are separated by a distance of 1 meter. So what will be the gravitational force of attraction between these two books?
For that, let's use our formula F equal to g m1 m2 by r square. So plugging in the values, we get force as 6.67 into 10 to the power minus 11 Newton. So how much is that?
It's going to be 0.000, so we have 10 zeros in there, 667 Newton. So it's a really tiny value. Now, will these two books eventually move towards each other?
The answer is no. And it's because this tiny force is overwhelmed by the force of gravity. And of course, there's friction of the table involved. In fact, gravitational force is the weakest force in nature. Let's place the concepts we have learned so far on our concept board.
Here is a list of the characteristics of the gravitational force. Let's look at each one by one. 1. The force is always attractive. We know that a magnet may attract or repel another magnet. But the gravitational force between two masses is always attractive.
For example, if this is my Sun and this is my Earth, we know that the Sun attracts the Earth. But did you know that the Earth is also attracting the Sun with this gravitational force? 2. Gravitational force is force at a distance.
So there is no need of any contact. We know that the Earth is far away from the Sun. Similarly, when you drop a ball, the earth pulls it down with the gravitational force.
But there is no contact between the ball and the earth. 3. The two forces are equal and opposite. So let's say for example, the sun pulls the earth with a force of 1 billion Newton. So what is the force of the earth on the sun?
That's right, it's going to be 1 billion Newton. But then the question is, why is the earth only spinning around the sun? It's because of the smaller mass of the earth compared to the sun. 4. The forces are independent of the intervening medium.
We know that there is no medium between the sun and the earth. It's just vacuum. But even if we filled it with an ocean, it wouldn't matter. The force would be unaffected.
Or to be more precise, the center of masses of the two bodies. 7. It's a long-range force. So as you keep increasing the distance between two bodies, the force keeps decreasing according to the inverse square law.
But the force never becomes zero. So all the things in the universe, the sun, the planets, the stars are attracting you and you are also attracting them. 8. Weakest force in nature. As we discussed before, gravitational force is the weakest force in nature, compared to other forces such as electrostatic, magnetic and nuclear forces. Let's pin the characteristics of gravitational force on our concept board.
I hope the concept of gravitation is crystal clear to you now. As we learnt in this video, everything is pulling everything. Hey, what's happening? Oh, that's not gravitational force. It's my friend tossing these.
And do remember to like, comment and subscribe. and share this video and subscribe to my channel and do check out my website manochacademy.com for more videos like these and for the quiz and the top 3 questions on this video. Thanks for watching.