The upward force that water exerts on objects is called buoyancy.

Here's a breakdown:

* Buoyancy is the upward force that a fluid exerts on an object that is submerged in it.

* This force is caused by the difference in pressure between the top and bottom of the object.

* The pressure at the bottom of the object is greater than the pressure at the top because the water at the bottom has to support the weight of the water above it.

* This pressure difference creates an upward force that opposes the object's weight.

Archimedes' Principle is a fundamental law that describes buoyancy:

* "An object submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces."

This means that if an object displaces 100 grams of water, the buoyant force on that object will be 100 grams.

Buoyancy is what allows ships to float, hot air balloons to rise, and fish to swim.