# Super-elasticity and infinite series

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Physics problems are often greatly simplified for new students. We assume negligible friction and perfectly elastic collisions. In some problems, the assumption of negligible friction might be reasonable. But students have a harder time understanding what perfectly elastic looks like. When they see it, it looks crazy, as I've found when I should the video below.

Three identical steel balls are dropped on 3 different surfaces: steel, titanium, and a specially produced metal alloy with the trade name LiquidMetal. LiquidMetal is in fact a solid, but it is a glass, in the sense that it does not have crystal structure like most metal we encounter. It happens to have super-high elasticity, returning nearly all of the energy to the bearing after each bounce.

You may want to turn the sound off for the first 45 seconds of bouncing, as it is mostly a sales pitch for the product. But definitely listen to the last part, as the ball continues bouncing.

If an object is dropped from a height , and rebounds to a height , then we say it has coefficient of restitution 

Can you estimate the coefficient of restitution for LiquidMetal using what you observe in the video? How many ways can you think of to do this?