How Does Ball Height Affect Velocity in Newton's Cradle?

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Discussion Overview

The discussion revolves around the dynamics of a Newton's cradle, specifically how the height from which balls are released affects their velocities at the point of impact. Participants explore the relationship between gravitational potential energy (GPE) and kinetic energy (KE) in the context of this mechanical system.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions whether the balls would have different velocities at the point of impact due to falling from slightly different heights, suggesting that more GPE would lead to more KE.
  • Another participant counters this by stating that since each ball is suspended from identical strings, they would rise and fall the same distance, implying they would have the same velocity upon impact.
  • A later reply acknowledges the initial question but asserts that the outward ball has the highest amplitude, leading to the greatest horizontal speed at the bottom, yet it cannot exceed the speed of the ball in front of it, resulting in both moving at the same speed.
  • One participant later agrees with the counterargument, reinforcing that both balls have the same amplitude and thus the same speed, as they are identical pendulums.

Areas of Agreement / Disagreement

Participants express disagreement regarding the effect of height on velocity, with some asserting that the balls would have the same velocity while others initially propose that differences in height could lead to different velocities. Ultimately, there is a shift towards agreement on the idea that the balls move at the same speed.

Contextual Notes

The discussion does not resolve the initial question about the impact of height on velocity, as it transitions to a consensus on the identical nature of the balls and their motion.

Who May Find This Useful

This discussion may be of interest to those studying mechanics, particularly in understanding energy transformations in pendulum systems and the behavior of Newton's cradle.

adamg
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if you have a Newton's cradle consisting of, say, 5 balls, and you displace 2 of these to the left and let them go, we say they hit the others with velocity v. I was just wondering if the balls would have different velocities at the point of impact since they will have inevitably fallen from slightly different heights (i.e more GPE = more KE?) Does the back one speed up more and then just push the second one so they do have the same velocity? thanks.
 
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adamg said:
since they will have inevitably fallen from slightly different heights (i.e more GPE = more KE?) .
I don't know why you say that. Each ball is suspended from its own identical string. Pull 2 aside by some distance, they both rise the same distance.
 
adamg said:
if you have a Newton's cradle consisting of, say, 5 balls, and you displace 2 of these to the left and let them go, we say they hit the others with velocity v. I was just wondering if the balls would have different velocities at the point of impact since they will have inevitably fallen from slightly different heights (i.e more GPE = more KE?) Does the back one speed up more and then just push the second one so they do have the same velocity? thanks.
The most outward ball has the highest amplitude so it should have the greatest horizontal speed at the bottom. But it can't go any faster that the one in front of it, so it pushes it forward and they both move at the same speed.

Edit: On second thought, I think Krab is right. They both have the same amplitude so they both move at the same speed. They are suspended from their own strings so each ball is an identical pendulum.

AM
 
Last edited:
yeah thanks, just been messing around with one i found and your right!
 

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