Question

when water filled tumbler is a placed on a tray and turned water spills. why ?

Answer 1

This is due to inertia of rest. When the tray is moved or turned quickly, the tumbler which is in contact with the tray moves with the tray as it is in contact with the tray. But, the water in the tumbler tends to remain in it's state of rest and thus spills when it tries to remain in the same position.