After this background on pressure and density, we are now ready to introduce the forces due to fluids. So let's start with upthrust, also known as buoyancy.
Here is a simple experiment for you to do in the bath. Try pushing a hollow ball under water. What do you feel? You should feel a force trying to push the ball back upward. This is the upthrust force. Now let go of the ball. What happens? It pops back up and oscillates at the water surface before settling down. You will create such an effect soon.
Upthrust is also responsible for making us feel lighter in the swimming pool or bath. It acts upward, opposing the force of gravity.
What causes upthrust? The physical origin of upthrust is the difference in pressure that exists ...