Stacked Ball Drop
Why Physics Stack Exchange recommends it
Physics Stack Exchange answerers point people to it as a clear visual demonstration of momentum transfer in stacked collisions, used for questions on collisions, Newton's cradle and supernova energy.
Recommended by 3 people across 3 different months, 2015 to 2026.
What it is
A short Physics Girl demo of dropping a stack of balls so that the top ball rebounds far higher than the drop height. It explains the result as momentum transfer between colliding balls and compares it to how a supernova throws off its outer layers. Hosted by Dianna Cowern, with trampoline footage and NASA space images.
Cited in 1 Wikipedia article, including Bouncing ball.
What people said
Recommends userLTK · 2015-07 · Physics Stack Exchange · on “When an object plunges into water, what is the maximum height a droplet from splash can reach?”
On the water-splash, here's a video that I think explains what happened. [this video] (the 3 balls, not the double bounce on the trampoline). The Newton law of conservation of energy says that energy is concerved, so a share of the energy of the drop transfers to the energy of the splash. Figure you drop it from 1/2 meter and the mass is 0.2 KG (about 7 OZ). Do a little math and 1/2 * 9.8 * .2 = .98 Joules, or about 1 joule of energy. How high a splash can 1 joule make in still water, well, it depends. The energy is converted into 3 different types of energy, wave energy, which is likely the biggest share, splash energy (#2), which depends on a few factors like the shape of the object, depth of t
Recommends MS-SPO · 2023-03 · Physics Stack Exchange · on “How does Newton's cradle actually work?”
As @Steeven remarked already: Ad #1 and #2: $\vec p = const.$ You may want to review the video Stack of balls [this video] from this perspective, to change perspective. Though it are inelastic collisions, violating the "const." condition, you still can explain it. If easier, replace by hard balls, e.g. on a billard table with diffently sized balls. Ad #3: As matter also has wave properties it's a microscopic view, which leads to the same result. E.g. if you lift one ball, collision point is between 1st and 2nd. There is a deleay of $1+1=2$ balls between both waves, which meet again at the $(n-1)$ -th ball at the other side.
Recommends RC_23 · 2025-05 · Physics Stack Exchange · on “Do the remnant cores of supernova core explosions exist in a state of ultra-lowered gravitational energy?”
This demo [this video] explains it better than any words could. The overall answer to both parts of your question is Yes. The massive decrease in gravitational potential energy due to the collapse is transformed into high kinetic energy of lighter mass elements that are ejected, and provides the activation energy for fusion of heavy elements. This really is not too divorced from our everyday experience. Imagine you drop a piano off of a 10 story building. Right before it hits the ground, it has a lot of kinetic energy, as a result of losing its gravitational potential energy. When it hits the ground, a lot of structural bonds will suddenly acquire the energy needed to break. And you will probably
Cites BowlOfRed · 2017-02 · Physics Stack Exchange · on “Can a collision of 2 objects result in one object having a higher velocity than either object had before they collided?”
Is there a set of 2 velocities v1 and v2 (rate and direction) and start time and start position such that the balls collide and the result is that either one of the ball's velocities is greater than v1 and greater than v2? For a single pair of equal mass objects, the answer is no. If we look at a collision of two masses in the frame where their center of mass is at rest, each ball will depart with the same speed (or less) that it arrived with. If we look at the collision in any other frame, then any boost we give to one of the outgoing objects simultaneously boosts the other incoming object. So you can't increase the speed that way. But if the objects have unequal mass (or you have more than
Cites MichaelK · 2018-01 · Physics Stack Exchange · on “How to hit a baseball or softball further?”
No, this will not improve your hitting distance Yes, it is true that if two objects collide — at least partially elastically [LINK] — and one one object is heavier than the other, then the heavier it is, the faster this will propel the lighter object [this video] . No, this does not have any relevance here. At the moment of impact between the bat and the ball, your hands and body are not part of that system. The bat has momentum and inertia; you do not. Your arms have momentum, yes, but your wrists are too flimsy and weak to be able to handle the force that would be needed to transfer any of that momentum from your arms, through the bat, to the ball. This in turn means that any backpack you wear
Cites gpuguy · 2019-10 · Physics Stack Exchange · on “Conservation of momentum: Collision involving Tenis ball on top of Basket ball”
I am asking about this video [this video] where The Physics Girl drops a system of balls from a height. I am trying to estimate the velocities just after the collision using the law of conservation of momentum. And I proceed as below: Consider the system as comprising of two balls (1: tennis ball, mass $m$ , and 2: basketball, mass $M$ ). Now initial momentum ( $p_i$ ) is $$p_i = m u_1 + M u_2 = 0,$$ as the ball is dropped from rest. The final momentum after the collision $p_f = m v_1 + M v_2.$ By law of conservation of momentum $p_i = p_f$ $$ 0 = m v_1 + M v_2 $$ or $$v_1 = - (M/m)v_2 $$ Is this explanation correct? If so what is the meaning of negative sign?
Cites naturallyInconsistent · 2026-01 · Physics Stack Exchange · on “How does a water jet form when dropping a cup of water?”
The behaviour is very reminiscent of the stacked ball drop [this video] that is quite commonly found being treated in first year university mechanics.