I was wondering about the conditions for an ideal newtons cradle.
Under regular circumstances, the collisions are inelastic and a newton's cradle dissipates energy in various forms like heat, friction, sound, and also faces air resistance.
Suppose we take the cradle in vacuum and minimize air resistance how can we eradicate the rest of the energy dissipation?
Are there any perfectly elastic materials we could use?
First of all, there are no elastic materials found till date and it will be like that either for eternity or a very long time.
Secondly, you told that we take the cradle in vacuum, thus zero air resistance and friction. (I have no idea why you wrote minimising air resistance when it is already in vacuum.)
And, then there is only one major loss of energy (and, countless small ones) that is sound. Although, you can't hear the sound because it is in vacuum, it doesn't mean that there is no sound produced. You can't make it zero, as there is sound where there is collision and so goes for the tiny heat.
Also, don't just concentrate on collisions, even the strings are inelastic.
Or, in most simple words, you can't reduce these to zero.
Suppose we take the cradle in vacuum and minimize air resistance how can we eradicate the rest of the energy dissipation?
The short answer is we can't.
For one thing, there is no such thing as a perfect vacuum. Even in interstellar space there are still a few hydrogen atoms per cubic meter (re Wikipedia article on Vacuum).
For another, at the macroscopic level (e.g., the balls of Newton's cradle), there are no perfectly elastic collisions. There will always be internal friction losses due to inelastic deformation.
Bottom line: If you could eliminate all dissipative losses of energy you would create a perpetual motion machine, in this case perpetual motion of the third kind. This is a machine that completely eliminates friction and other dissipative forces to maintain motion forever due to its mass inertia. No such machine exists.
Hope this helps.
