 Let's solve a couple of questions on forces and motions. For the first one we have a man who throws a ball from the top of a building. The ball slows down until it reaches its highest point then it speeds up as it falls. How does the net force on the ball change as it moves through the air? We need to choose one answer out of these four options. As always, hit pause and try this one on your own first. Okay, hopefully you have given this a shot. Now first let's try to represent what's happening over here. So we have someone who is throwing a ball from the top of a building and this could be the trajectory of the ball. It reaches a maximum height which is this point and then it starts falling down and it speeds up as it falls. Now we need to think about how is the net force changing. So let's try and think about the net force from the perspective of the ball. When the ball is in the hand of the person then at that point there will be a force experienced by the ball and that force will be from the person itself. So there will be a force in the upward direction. This will be the F by the hand of the person. So there's a constant force experienced by the ball as long as the ball is in the hands of the person and even when the ball is in the hands of the person and the ball is experiencing this force, there is one more force that the ball is experiencing at this moment and that force is really the force of the force of gravity. So this is force of gravity. We can place this at the top. This is a situation when the ball is in the hands of the person and now when the ball leaves the hand, there is one force which disappears really and that would be that would be the force due to the hand because the hand itself disappears, right? When the ball leaves the person's hand, there is no interaction between the ball and the hand so there is no force that is exerted by the hand on the ball. So the force due to the hand disappears when the ball leaves the person's hands and there is one force that remains which is the force due to gravity. So at all of these instances, at all of these instances that you see in the diagram, there will be one force that is constantly acting that is constantly acting on the ball and that will be a force due to the gravity. And we can assume that the ball is very close to the surface of the earth so that the gravitational force doesn't really change. It's not like the person is throwing the ball outside the earth's atmosphere where the gravitational force also decreases. We can assume that the ball is close enough so that the gravitational force is constant throughout and that means that the net force, the net force on the ball remains constant because we are not assuming any form of air resistance, any form of friction from the air which can oppose the motion. So the right option here is option option A. Now let's let's look at one more question. So here we only know that the particle is moving upwards for some particle which moves upward. Which of these is true for the direction of the force acting on the particle? We need to choose one answer out of these three options. So the only information that we have is some particle that is moving upwards. It has a velocity in the upward selection. Let's look at the options. First option is that information is not sufficient to find out the information about the forces and second is there is more downward force on the particle than upward. Let's think about this. Let's think about option B. If there is more downward force, if there is more downward force than upward force then there will be a net force in the downward direction. There will be f net in the downward direction. Now this could be true because we saw it in the last question itself when the person threw the ball upwards. The time which the ball took to reach the maximum height from the top of a building, the ball was moving upwards and the constant force, the net force was only in the downward direction which was the force due to gravity. So this could be true but think about the case of a rocket for instance. If there is a rocket and let's try to draw a rocket. So if this is a rocket and there is all these exhaust gases coming out. So in this case the force due to the exhaust gases, that will be in the upward direction which will be more than the force due to gravity. Which will be in the downward direction. So the net force is in the upward direction but still the movement, the motion is also in the upward direction. So second statement is not necessarily always true for the case when the particle is moving upward. If the particle is moving upward, there is a possibility that the force upwards is more than the force downwards. So it's not always true. Option B, this will not always be true. So this is wrong. And in a similar line of reasoning, we can say that option C is also wrong because we just saw the case when the ball was thrown upwards. There was a force of gravity which acted on the ball as the ball went up. There was a constant force of gravity but still the movement, the motion, the velocity was in the upward direction of the ball. The ball was going up. There was a force downwards. The net force was down. But still the motion was up. This really tells us that the velocity of an object at any instant does not tell us anything about the forces. It does not tell, it does not give us any information about the forces. Forces can only tell us the acceleration, the change in velocity. But we can't really relate velocity with forces, at least, at least in the directions that they are. So for this one, option A is the correct option because information is not sufficient to find out the information about the forces. We just saw that these two cases are completely possible and no statement out of these two will always be true for the case that the particle is moving upwards. You can try more questions from this exercise in this lesson and if you're watching on YouTube, do check out the exercise link which is added in the description.