Ideas on How This Exhibit was Designed?

[WorldWiz]

TL;DR Summary

How do the ball bearings in this video bounce so well off of steel glockenspiel bars?

Watching this exhibit from years ago () led me to think that ball bearings will bounce really well from steel glockenspiel bars, but that wasn't the case when I tested this myself with a stainless steel ball bearing and a steel glockenspiel bar. Granted, I was just propping up the bare glockenspiel bar with two finger spaced out at the two nodal points (ie holes) of the bar, but I still got <5% bounce height, so I think there's probably another factor that I'm not considering that's making the exhibition work.

My best guess is that the ball bearings in the video are made out of a lighter material (hence I chose this subforum) like titanium, maybe, but does anyone else have any ideas on this? Perhaps the type of material of the glockenspiel bars is also important, if it's a stiffer material that won't absorb/dampen the energy carried in the ball bearing? Thanks.

 

[berkeman]

Granted, I was just propping up the bare glockenspiel bar with two finger spaced out at the two nodal points (ie holes) of the bar, but I still got <5% bounce height

You were supporting the metal bars with your fingers? That damping is probably where the energy got dissipated. Still, a 5% rebound is remarkably low...

 

[Baluncore]

TL;DR Summary: How do the ball bearings in this video bounce so well off of steel glockenspiel bars?

...Granted, I was just propping up the bare glockenspiel bar with two finger spaced out at the two nodal points (ie holes) of the bar, but I still got <5% bounce height,...

The bars will need to be held down onto a hard knife edge, at their exact nodal points, to prevent loss of energy at each fulcrum.

...Perhaps the type of material of the glockenspiel bars is also important,...

Yes. Select a material that will ring like a bell, test any small sample you find.

Some materials contain big crystals, of differing structural chemistry, with significantly different acoustic impedance. Those materials sound dull and do not ring. Metal alloys are like rocks. Most rocks sound dull when you hit them, but some will ring efficiently if they are not fractured.
https://en.wikipedia.org/wiki/Phonolite

Avoid some stainless steels, aluminium, zinc or lead alloys that have been allowed to cool slowly. Select instead hard alloys that are close to eutectic composition, and that have been cooled rapidly.
https://en.wikipedia.org/wiki/Eutectic_system

When bouncing a ball, surface finish will be important. You might chrome plate the bars, or fine polish the surface of a material that will not oxidise. You don't want to go dropping a ball onto a surface of soft oxide or powder.

 

[WorldWiz]

The bars will need to be held down onto a hard knife edge, at their exact nodal points, to prevent loss of energy at each fulcrum.

Yes. Select a material that will ring like a bell, test any small sample you find.

Some materials contain big crystals, of differing structural chemistry, with significantly different acoustic impedance. Those materials sound dull and do not ring. Metal alloys are like rocks. Most rocks sound dull when you hit them, but some will ring efficiently if they are not fractured.
https://en.wikipedia.org/wiki/Phonolite

Avoid some stainless steels, aluminium, zinc or lead alloys that have been allowed to cool slowly. Select instead hard alloys that are close to eutectic composition, and that have been cooled rapidly.
https://en.wikipedia.org/wiki/Eutectic_system

When bouncing a ball, surface finish will be important. You might chrome plate the bars, or fine polish the surface of a material that will not oxidise. You don't want to go dropping a ball onto a surface of soft oxide or powder.

Thanks for such a detailed guide. This gives me more confidence that my project can still work.