Extending run-time of Newton cradle?

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In summary, the conversation discusses the idea of placing a Newton's cradle in a vacuum to observe its motion in the absence of air resistance. It also suggests conducting experiments with different materials and shapes to determine the effects of damping and aerodynamic forces on the system. The issue of the duration of collisions and the speed of sound in the material is also mentioned as a factor in the cradle's motion. The conversation provides a website for further information on the topic.
  • #1
I got an idea the other day in class about Newton's cradles.
I was wondering if you put one in a vacuum and started it, would it run for longer, as opposed to being in normal conditions because of sound's inability to travel through vacuums etc? Would anyone be able to clarify because I was thinking of basing an EEI on this?
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  • #2
There are at least two ways that the system loses its kinetic energy.

One is air resistance, friction between the wires and the supports, etc.

The other is that when the stress level changes in the materal, some of the energy is converted into heat.

You could separate those two effects by swinging the cradle like a pendulum, with no impacts, and doing the usual Newtons Cradle demonstrations. You might be able to get a theoretical result for the damping caused by the aerodynamic force acting on a pendulum made with single sphere. (Hint: don't try to solve the equations of motion for this. Assume you have the same simple harmonic motion as for a pendulum without damping, and find the amount of work done by the drag force in one cycle of oscillation).

If you did both of those in air and in a vacuum, you might be able to deduce how much of the damping comes form the material and how much from the air. You could also try using different materials for the balls of the cradle. Most structural metals have similar (and low) levels of hysteretic damping, but rubber or plastic, probably behave differently.

It might be interesting to compare spheres and cubes, with the whole face coming into contact compared with a "single point". For the cubes, the stress in the materal would be lower becaise of the bigger contact area, and that might result in lower hysteretic damping. But there might be more aerodynamic damping because you have to "pump" all the air out of the gap between the cubes and "suck" it back in again, losing energy because of the viscosity of the air.

Hope that gives you some ideas to think about!
  • #3
There's also the issue of the duration of collisions versus the time it takes for the force of the collisions to propagate through the balls (speed of sound for the material in the balls). The result is that the outcome isn't quite the "perfect" outcome you'd like to have with a Newtons cradle. I'm not sure if this is why the "inner" pack tends to start swinging over time, or why the outer ball(s) bounces back a bit instead just stopping when they collide with the "inner" pack. This website has a lot of info:


1. How can I make the Newton's cradle run longer?

The run-time of a Newton's cradle can be extended by increasing the length of the cradle's strings or by using heavier balls. This will increase the potential energy of the system and make the balls swing for a longer period of time.

2. Can I use magnets to extend the run-time of a Newton's cradle?

No, using magnets to extend the run-time of a Newton's cradle will not work. The magnets can interfere with the motion of the balls and cause them to stop swinging sooner.

3. How does the angle of release affect the run-time of a Newton's cradle?

The angle of release does not have a significant effect on the run-time of a Newton's cradle. It may slightly alter the trajectory of the balls, but it will not make a significant difference in the run-time.

4. Is it possible to extend the run-time of a Newton's cradle indefinitely?

No, it is not possible to extend the run-time of a Newton's cradle indefinitely. The motion of the balls will eventually slow down due to friction and air resistance, causing them to come to a stop.

5. Can I add more balls to a Newton's cradle to increase its run-time?

Adding more balls to a Newton's cradle will not necessarily increase its run-time. The additional weight may cause the balls to swing for a shorter period of time. It is best to stick to the recommended number of balls for optimal run-time.

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