## Subtitles section Play video

• Check out how high these different balls

• bounce-- the basketball, the super bouncy ball, and the golf

• ball.

• Now, I'm going to try the golf ball on top

• of the bouncy ball on top of the basketball,

• and then I'm going to explain how

• it's related to a supernova.

• Did you see that?

• Probably not, so here it is again.

• The golf ball bounced to 28 feet.

• We dropped it from about 3 and 1/2 feet, so it went up 800%

• of its dropped height.

• In fact, if you consider that by itself-- the golf ball bounces

• about 70% of it's dropped height--

• it went as high as if it had fallen from 40 feet up.

• That is awesome.

• So how can we get the golf ball to bounce up

• with that much energy?

• Let's simplify it to these two balls.

• When you drop them individually, each ball

• starts out with some potential energy

• from the height of the drop.

• As the balls hit the ground, some energy

• goes into heating up the ground, and some

• goes into heating the ball.

• Because that energy left the ball system,

• you can't get back up to the same height.

• But when you combine them, the tennis ball

• goes higher than its dropped height, way higher.

• Where does it get the extra energy?

• As the basketball bounces, it compresses, storing

• elastic potential energy.

• As it releases, it springboards the tennis ball upward

• just at the right moment.

• This is like the double bounce on a trampoline

• when you jump right before someone else.

• You prepare the elastic of the trampoline

• by stretching it and storing energy, which can then

• bounce the jumper even higher.

• In the same way, the basketball stores energy

• in its compression and is able to push the tennis ball,

• but just like the double bounce preparer,

• the basketball can't go as high.

• You can see that here.

• It bounces even less when three balls are dropped together.

• Also during that transfer of energy,

• some momentum transfers from the basketball to the tennis ball,

• and since the basketball starts with way

• more momentum because of its larger mass, the tennis ball's

• velocity increases by a lot.

• And it flies up, up, and away.

• Now, back to the triple super ball bounce.

• Now, do you get the energy from the basketball's bounce being

• transferred into the bounce of the super bouncy

• ball, which is then transferred to the golf ball's bounce.

• You put the same amount of energy or momentum

• from two more massive objects into a smaller object,

• and it will go much faster, epic,

• just like the explosions of a supernova, which

• may seem unrelated.

• But what we just did is analogous to the process

• that occurs during the explosion of a supernova.

• Just like our more massive basketball transfers momentum

• to the smaller balls, energy from the dense core

• of the supernova is transferred in a shockwave that

• moves through the star to the less dense layers

• and accelerates them outward at a super high velocity.

• More massive or denser layers in the core of the supernova

• begin to collapse when fusion stops there.

• The collapse is halted when the neutrons in the core

• actually touch, sort of.

• This causes the implosion to rebound and bounce outward.

• You end up with a dense core left behind

• and these wild outer shells of star exploding outward, pretty

• cool.

• And, of course, if you try this at home, which you should,

• you have to make sure the balls are perfectly vertically

• aligned because any off centeredness gets amplified

• by the two points of contact, which

• is why we sadly couldn't get the quadruple tower of balls

• to work.

• But if you put a little ring of hot glue or something

• similar on the balls, it helps to balance them.

• Happy physicsing.

• [MUSIC PLAYING]

Check out how high these different balls

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B1 US ball bounce golf ball energy tennis ball golf

# Stacked Ball Drop

• 263 9
Samuel posted on 2018/07/21
Video vocabulary