Mote

every push is paid in mass.

tap where you want to go and a piece of you squirts out the back; eat the green, avoid the red, shrink with each push

A body floating in fluid has no floor to push against, so it moves only by throwing part of itself the other way. Momentum is conserved: the faster you want to go, the more of yourself you have to spend.

Concepts: momentum, conservation, physics.

An interactive you play with one thumb, on Wundr.