What is upthrust force? Is is the pressure difference or just pressure x Area at the bottom of the surface? How does upthrust force change with depth in liquid?
One often observe that our body feels lighter while taking a swim in the pool.
When drawing water from a well, the bucket feels lighter to us till it is partially or fully immersed in water.
We can say, when immersed in water or any other fluid, the body experiences a force from the downward direction to upward direction which is responsible for the decrease in its weight.
I think you are calling this force as upthrust.
Upthrust is the force that causes objects to float.
It is the force exerted on an object that is partly or wholly immersed in a fluid and is caused by the differences in pressure acting on opposite sides of an object immersed in a static fluid.
When we dip an object in a fluid, an upward force is experienced by the object. This force is applied by the fluid on the object which makes it to, rise up and is called the upthrust or Force of Buoyancy.
The value of this force is precisely equal to the amount or weight of the liquid displaced.