What is "tumbles"

Usage examples of "tumbles".

For forty miles, up as far as the little border post at Kazungula, the wide river tumbles through rapids and then spreads into dawdling shallows.

Phegeus is flung backward off the chariot, striking the ground and cartwheeling several times, the spear breaking off and splintering as the corpse tumbles to a stop in the dust of the chariot he had been riding five seconds before.