Wobble

wait for the swing. then let go.

drop blocks from a swinging crane and stack a tower that sways, leans and topples

The crane is a pendulum and the block keeps a third of its sideways speed. A block that lands off-centre leans the tower, and the tower falls when the weight above any level passes that block's edge.

Concepts: balance, pendulum, gravity.

An interactive you play with one thumb, on Wundr.