A container of water is placed on weighing scales. What happens if you put your fist into the water without touching the container?
The scales show an increase in weight.
How does it work?
In water, bodies experience buoyant forces, which are strictly speaking upward forces. Newton discovered that for each force there is an equal and opposite force produced: Every action has a reaction. The water pushes the fist upwards due to buoyancy so the fist presses the water and the scales downward as a counterforce. This causes an increase in weight registering on the scales.
