Why does bounce happen

At full rebound, the ball has left the surface, and its velocity vector still points upward, though shrinking steadily due to the acceleration or deceleration due to gravity. Following this step, the ball with reach peak at a new step, one where its velocity vector is zero, and the only force acting on it is gravity.

The case of the bouncing ball above was simplified to remove any other forces like air resistance, imperfect elasticity, spin, friction, and the force from an initial throw, among others. All this means that bouncing ball physics gets more complicated from here. When balls have any spin, as they usually do when thrown, and when the surface they hit isn't frictionless, the spin of the ball reverses from before to after impact.

This is due to the force of friction. Assuming 2-dimensions for theory's sake, you can observe the reaction below. As the ball impacts with a spin in one direction, the friction force F counteracts the spin of the ball. Or rather, the friction force is always opposite the direction of the slip velocity between the spinning ball and the surface.

Since the friction force is opposite of the ball's spin, it torques the ball in the other direction. It also causes the path of the ball's bounce to skew in the direction of the friction force.

In simplified terms, when a ball spins in one direction when it hits a wall, the friction between the ball and the wall overcomes the spin so much that it reverses its spin direction.

This spin reversal doesn't happen if the ball and the wall's coefficient of friction aren't high enough. The coefficient of friction varies by material and surface and is essentially a number that indicates how grippy a surface or material is.

In real life non-ideal scenarios, bouncing balls lose energy and eventually come to a stop. This is all due to the forces we ignored in the first example.

When a ball hits a wall or surface, it makes a noise, which is a loss of energy from the ball's bounce. It also will generate some amount of heat, another loss of energy. Friction from the wall will cause energy loss as well as air resistance while the ball travels. These include finding out how much sugar certain drinks contain, how to keep bones strong and healthy and even making a model lung! Try this fun investigation into skipping rope lengths from Science Buddies.

We loved seeing them in action! Science Sparks Wild Sparks Enterprises Ltd are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources.

Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources. These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

Your email address will not be published. What do you notice? The vertical and horizontal COR also depend on the elastic properties of the surface.

For example, if the surface is rubber rather than concrete then the horizontal COR will be larger and the ball will spin faster after it bounces.

The following images were taken from video film of a hollow rubber ball incident obliquely on a smooth block of granite. The vertical dashed lines pass through a fixed point on the granite surface. Equator lines were drawn on the ball to measure its rotation during the bounce. The images show two interesting results. The first is that the bottom of the ball gripped the surface during most of the bounce. The bottom of one equator line remained firmly attached to the dashed lines, rather than sliding forwards.

The ball moved forwards like a bulldozer or an army tank on catterpillar track. The second is that the ball first leans forward in frames 1 and 2, due to its high initial speed, then it leans backwards in frame 4.

The ball therefore vibrates sideways, and causes the friction force on the bottom of the ball to reverse direction. As a result, the ball spin at first increases during the bounce then it decreases. The angle shown in each frame is the change in rotation angle from one frame to the next.

Note how clay sticks to the ball and is then spun off. The grass here was longer than normally seen at Wimbledon. Grass is a faster surface than clay, even when the grass is long. You can work out the bounce speed, spin and angle yourself from this film.

The hoop slides then grips before bouncing, in the same but in a much more obvious manner than a ball. It is also obvious, especially in bounce2, that the normal reaction force does not act through the centre of mass and therefore exerts a strong torque on the hoop, reducing the spin rate. The same effect occurs with spherical balls. If one part of a ball stops rotating while the rest of the ball continues to rotate, what then happens to the ball? The hoop film here helps to answer that question.

The hoop behaves as a system of inter-connected particles rather than as a rigid object. The angular momentum of the system is well-defined, even though the angular velocity and moment of inertia are not. Four different strings showing string movement: String1 String2 String3 String4. You need to advance one frame at a time to see the movement. Note that strings return to their original position very quickly, at least when new, thereby enhancing the spin of the outgoing ball as explained in the pretty picture below.

When a ball bounces, the force on the ball increases to a maximum when the ball compression is a maximum, and then drops back to zero at the end of the bounce period. The force varies in a sinusoidal manner. When a spring bounces on its end, the force remains constant in time while a compression wave travels up to the top end, reflects, and travels back to the bottom end. Then the force drops to zero and the spring bounces.