A basketball and a small ball are stacked and dropped simultaneously. Upon collision with the ground, energy from the bottom ball transfers to the top one and it bounces higher than it would alone.
Equipment:
- Basketball
- Smaller rubber ball
Demo:
- Drop each ball from the same height individually. Notice how far each ball bounces back.
- Hold the rubber ball on top of the basketball and release them at the same time.
Note: Be careful when dropping the balls; the rubber ball should be as centered on the basketball as much as possible so that when both of them are released, the rubber ball can bounce straight up as opposed to outwards.
Explanation:
There are two main effects that are occurring when you drop these two balls. One is a transfer of momentum and the other is a transfer of elastic potential energy to kinetic energy.
-
- Momentum Transfer: Right before the basketball hits the ground it has a momentum of
, where
is the mass of the basketball and
is its velocity. Theoretically if the basketball has a perfectly elastic collision with the ground we just have to worry about the collision with the rubber ball on top. The rubber ball has a momentum of
. If the basketball and the rubber ball have a perfectly elastic collision. Since the basketball has a much larger mass it therefore has a much greater momentum. This momentum transfer is then given by the equation below:
- Momentum Transfer: Right before the basketball hits the ground it has a momentum of
Modeling Supernova Explosions
This demonstration can be used to model supernova explosions. A supernova is a powerful and luminous explosion of a star. It happens when the star has reached the end of its life. In the supernova, the core of the star (represented by the basketball in the demonstration) undergoes a catastrophic contraction, just like the basketball being dropped and rebounding off the floor. The outer atmospheric layers of the star (represented by the tennis ball) are less dense and take a bit longer to contract. When the core (basketball) rebounds, the atmospheric layers (tennis ball) are still in-falling towards the core.
Due to the transfer of momentum from the basketball to the tennis ball, the rebounding core meets the incoming atmospheric layers with enough energy to blow the atmosphere away from the star. This is similar to the tennis ball being propelled high into the air when it is dropped on top of the rebounding basketball. This ejection of the star’s atmospheric layers is what we observe as a supernova explosion.
Notes:
- Make sure the balls are fully inflated (use ball pump in drawer)