Answer this question about Newton's Third Law of Motion?

Question

When I drop a ball and it hits the ground, it's going to bounce because for every reaction there is an equal but opposite reaction. So the force of the ball coming back to me should be of the same force I dropped it, right? So now I'm confused as to why the ball doesn't bounce forever? Since the ball should be bouncing up with equal force and then falling again. It's like an endless loop. Obviously, this doesn't happen in real life, why?

Answer 1

What a variety of answers so far! Some correct and some utter dross...

Firstly, there is no "force of the ball" when you drop it, assuming you just release it. Gravity pulls down on the ball, and this causes it to accelerate towards the ground. When it hits the ground, gravity still exerts a downwards pull, but the floor now pushes up on the ball with a much larger force. So long as the ball is in contact with the floor, this force exists, and acts to accelerate the ball upwards. The size and duration of this upwards force depend on the material of the ball and floor. It is much easier to discuss what happens here if you use an energy argument (see next para).

When you release the ball it has Gravitational Potential Energy (GPE). As it falls, its GPE is converted into Kinetic Energy (KE) in its motion. As it falls through the air, some GPE is converted into heat due to air resistance. When it bounces, the KE is converted into Elastic energy stored by the squashed ball (and compressed floor), and some is also lost as heat (as the atoms of the ball and floor are squashed and squeezed). So not all of the initial energy will be available to be returned to the ball.

Hope that helps!

Cheers,
Ben

Answer 2

The reason is friction. As the ball passes through the air, drag slows it down a tiny bit. When it hits the ground, the impact causes it to deform, which is what gives it the elastic energy necessary to bounce back up. But as it deforms, it rubs against the ground, and friction somewhat inhibits the deformation, decreasing the elastic energy that will push the ball back away from the ground. Friction causes the ordered kinetic energy of the moving ball (ordered because the molecules in the ball move in the same direction) to be transformed into disordered kinetic energy, also known as heat.

Answer 3

Because there is a force of gravity pulling the ball towards the Earth as it is bouncing up, so it won't reach the original height when you bounce it. In order to achieve the same height, u need to add an additional force to cancel out the force of gravity.

Answer 4

The reason why the ball doesn't bounce continuously is because two forces act on it: air resistance force and the force of gravity.For the ball to bounce continuously without stopping,it has to be in an isolated system where the only force acting on it is the force of gravity.

Answer 5

well in a perfect world there would be nothing to stop the ball from bouncing forever but here on earth when you bounce the ball and it goes back up its fighting the force of gravity trying to pull it back down,wind resistance and friction,plus every time the ball bounces id deforms and in doing so gives off heat(a small amount yes but heat is energy) so its easy to see once you add all these things up that without some outside force being added the ball will eventually stop

Answer 6

The reason why a bouncing ballon on the floor does not obey Newton 'law of Inertia(that is continuous motion) is because of mass loss that the mass structure of the ball experience. As the Ball loses mass the Gravity energy between the ball and the floor changes.
Therefore momentum is not conserved because the mass structure of the Ball is not conservative. Only in a perfectly elastic system the mass structure is conserved.
So In complex mass structure The law of momentum conservation only applies if the mass loss is negligible during collison with another mass structure.

In the case of the ball it loses its energy of motion and at the same time aquires Gravitation potential energy. At that point the ball no longer bounces.As the motion of the ball is hindered due to the mass of the earth blocking its motion a force is born from the Earth pushing upward and an active Gravity force pushing down .So to every action(Power application) there is an equal and opposite reaction.=Newton's 3rd Law!

The law of conservation of momentum in reality only applies to micromass particle of light.
That is why in Einstein's Relativity theory, Momentum is not conserved.

Answer 7

It happens so becoz there is energy loss when ...the ball hits the ground and deforms on impact....air friction...gravity acting on it when it bounces up...these forces act every time the ball hits the ground and bounces back..so the ball loses energy with every bounce and comes to a stop after sometime.

Answer 8

Ignoring air resistance, you still have energy loss due to deformation of the ball on impact with the ground. Deformation counsumes energy and so the resultant bounce height is lower. So it will not quite reach the height it was dropped from.

If in vacuum, and inelastic collision, the bouncing should be forever.

Answer 9

Because the force of gravity on the ball continues to draw it down to the ground where it'll eventually cease motion altogether.

Aside from Newton's Law, the reason the ball bounces at all is because of the material of which its made. As it hits the ground, it rebounds with equal force in the opposite direction, but now it has gravity continuing to act upon it. That's why the rebound gets less high with each successive bounce.

Hope this makes sense.

Answer 10

Two things:

1. FRICTION! It's what prevents the age old quest forperpetual motion

2. Gravity (i.e. 9.81 m/s -1)

Simple high school physics!