# Explain when will upthrust change?

1. Aug 9, 2010

### starwars32

Hi.. Can someone explain when will upthrust change? cos i come across books saying that upthrust will not change when two objects of different density but same material are placed in the same fluid. I also come across that upthrust will not change when same objects are being transferred from liquid a of different density to liquid b of another density, the upthrust also will remain same. Can some one pls explain to me when and when will upthrust not change? Under wad conditions thanks!

2. Aug 9, 2010

### mgb_phys

Re: Upthrust

The upthrust is equal to weight of the fliud the object displaces - so it depends on the size (volume) of the object and the density of the fluid - thats all

3. Aug 9, 2010

### starwars32

Re: Upthrust

then does weight of an object plays a part? Next, if lets say for the same object, we put in fresh water of Density 1, we have an upthrust of U, if we put this object in sea water of Density 2, will we have a simliar upthrust?

Last edited: Aug 9, 2010
4. Aug 9, 2010

### sfsy1

Re: Upthrust

The weight of the object doesn;t affect upthrust, they are 2 different forces. And no upthrust will not be the same because the density of the fluid changed.

As said in the previous post, it's the volume of the object (i.e. the amount of fluid displaced) and the density that matters.

5. Aug 9, 2010

### mgb_phys

Re: Upthrust

The upthrust is normally defined as just the upward buoyancy force - the overall buoyancy, or apparent weight, will depend on the upthrust and weight.