Explaining Newton's Cradle: The Science Behind the Single Ball Effect

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Discussion Overview

The discussion revolves around the mechanics of Newton's Cradle, specifically addressing why only one ball emerges from the other side when a single ball collides with a group of balls. Participants explore concepts of momentum and energy conservation, as well as the dynamics of elastic collisions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions why only one ball exits the cradle after a collision, despite momentum being conserved in both scenarios where one or two balls could emerge.
  • Another participant asserts that the collision is elastic, implying that both momentum and kinetic energy are conserved, and suggests that the mathematics is straightforward for equal mass balls in one dimension.
  • A participant expresses frustration over realizing a concept only after articulating it, indicating a common experience in understanding physics.
  • One participant presents a related question about why two balls do not exit with twice the speed when two balls are pulled back and released, seeking clarification.
  • Another participant refers back to the previous explanation, suggesting that the answer remains consistent over time.
  • A participant inquires about the mathematical approach to solving the problem, indicating a desire for a more rigorous analysis.
  • One participant claims that there are multiple solutions that satisfy the conservation laws, hinting at the complexity of the situation.
  • Another participant provides a detailed explanation, suggesting that the behavior of the balls is due to the equal mass and the sequential transfer of momentum and energy, likening it to billiard balls. They also mention the effect of slight compression during impact, which introduces a delay in the movement of the balls.

Areas of Agreement / Disagreement

Participants express differing views on the underlying mechanics of Newton's Cradle, with some emphasizing conservation laws while others focus on the sequential interactions of the balls. The discussion remains unresolved with multiple competing explanations presented.

Contextual Notes

Some participants reference previous discussions on the topic, indicating that the understanding of the mechanics may evolve over time. There is also mention of the need for visual aids to clarify the explanations provided.

FulhamFan3
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Everyone here should be familiar with the office toy known as Newton's Cradle where a ball collides with a group of balls and a ball moves out the other side.

What I want to know is when a ball collides with the group why does only one ball come out? Why doesn't two balls come out at half the speed? I mean momentum is conserved in both situations.
 
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It's because the collision is elastic. So energy has to be conserved as well. The math is really easy for balls of equal mass in 1D.
 
yeah, I've been thinking about it for days but it's not until i type it in and send it that i realized this. Don't you hate it when that happens.
 
wait. i have a similar problem. in physics today, we asked the question, "if a person takes 2 balls and pulls back, and releases, why doesn't a single ball on the other side pop out with twice the speed?"
please help!
 
The answer is the same as it was when this was asked 5 years ago. Please read the above posting.
 
well how would one solve this problem mathematically?
 
Read post #2.
 
Yeah, the real explanation doesn't have anything to do with the conservation of anything for the system, of course those are followed but that isn't why it happens. It happens because one ball whacks another and stops because they have equal mass (just like a billiard ball), then the newly moving ball moves just a tiny bit and whacks the other one, then again, and again. Each ball that did the whacking is stopped because they have equal mass, or it transfers all of it's momentum and energy (just like a billiard ball). If you bring up two balls and let em go then two pop out, then ask, why does that happen? It is because of the same reason, the first ball whacks the other stationary ball, then the second moving ball whacks the newly stationary ball, blah blah, it is as if you dropped them separately, but only a tiny fraction of time apart. This needs a picture but I am too lazy to do it, but think about it.

The reason that the falling ball behaves as if it only hit one ball is because in the real world there is a slight compression of the balls on impact, so there is a delay between when the first stationary ball moves, and the next stationary ball etc.
 
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