For what is snapping of balls on the sand?
To check which one is heaver!
The same games plays physicists (but much more expensive)! If two balls are bouncing and are moving perpendicular, then they have the same mass. it theay are bouncing under sharp angle, than incoming ball is heavier than a target. Like on the photo below.
Bounced ball are alpha particles (helium nuclei with mass 4) in collisions with hydrogen nuclei (mass 1) - on the left photo, or helium (mass 4) on the right photo. This photo is from bubble chamber filled with molecular hydrogen (left photo) or He (roght photo). Source: H.Haken i H.C Wolf, Atomy i kwanty, PWN 2002.