Buoyant Force on Finger

What it shows

An object does not need to float in order to experience the buoyant force.

finger about to push against liquid in a cup

In this example we see a cup of water at rest on a pan balance. When the demonstrator pushes a finger down into the liquid, the buoyant force of the liquid pushes up on the finger with a force equal to the weight of the displaced water. The incompressible liquid pushes down on the balance as it pushes up on the finger.

water pushes on the finger, and the balance pushes against the water

Setting it up

A clear plastic cup of water works well. Food coloring is optional. A camera may be necessary in a large lecture hall. Dip the finger smoothly and slowly.