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Vincent Thacker
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Suppose, I'm dropping a rubber ball on the floor and it bounces back up. I'm trying to understand this by considering the forces, and not using momentum, collision, or energy.

Eventually, the ball would come to rest, due to dissipation of energy, and when that happens, the normal reaction of the floor on the ball would be equal to the weight of the ball, due to electrostatic force.

However, I'm wondering what happens before that. When the ball drops for the first time, it would bounce back up. There are three forces involved here, that are relevant. First is the normal force exerted on the floor by the ball (indirectly due to gravity). The second force is the normal reaction of the floor on the ball ( duedue to electrostatic repulsion  ). The third is the force of gravity exerted on the ball by the Earth.

Normally it is expected that the normal force should be equal to the weight, as is the case when the ball comes to rest. However, in this case, the initial normal force exerted on the ball, by the floor, is obviously more than the weight - hence the ball bounces back up. My question is, how is that so  ?

How can the normal reaction force be initially greater than the weight  ? Please tell me this, on the basis of the acting forces, and not using momentum conservation and energy conservation.

My intuition is that there is a fourth force working here, one that deforms the ball when it hits the ground. This force increases the normal reaction of the ground toward the ball, and makes it greater than the weight, and is the reason why the ball bounces back up. Each time the ball loses energy, so this deformation would be lesser and lesser, and the reason why the normal reaction would decrease after every bounce, until it becomes equal to the weight.

Please tell me if this explanation is correct for this situation. Moreover, please tell me, if this explanation is correct for collisions in general.

I'm trying to look at collisions from the force perspective, rather than the momentum perspective.

Thanks.

# What makes a ball bounce back up?

Suppose, I'm dropping a rubber ball on the floor and it bounces back up. I'm trying to understand this by considering the forces, and not using momentum, collision, or energy.

Eventually, the ball would come to rest, due to dissipation of energy, and when that happens, the normal reaction of the floor on the ball would be equal to the weight of the ball, due to electrostatic force.

However, I'm wondering what happens before that. When the ball drops for the first time, it would bounce back up. There are three forces involved here, that are relevant. First is the normal force exerted on the floor by the ball (indirectly due to gravity). The second force is the normal reaction of the floor on the ball ( due to electrostatic repulsion ). The third is the force of gravity exerted on the ball by the Earth.

Normally it is expected that the normal force should be equal to the weight, as is the case when the ball comes to rest. However, in this case, the initial normal force exerted on the ball, by the floor, is obviously more than the weight - hence the ball bounces back up. My question is, how is that so ?

How can the normal reaction force be initially greater than the weight ? Please tell me this, on the basis of the acting forces, and not using momentum conservation and energy conservation.

My intuition is that there is a fourth force working here, one that deforms the ball when it hits the ground. This force increases the normal reaction of the ground toward the ball, and makes it greater than the weight, and is the reason why the ball bounces back up. Each time the ball loses energy, so this deformation would be lesser and lesser, and the reason why the normal reaction would decrease after every bounce, until it becomes equal to the weight.

Please tell me if this explanation is correct for this situation. Moreover, please tell me, if this explanation is correct for collisions in general.

I'm trying to look at collisions from the force perspective, rather than the momentum perspective.

Thanks.