# Buoyancy of object in water

1. Jul 11, 2012

### malek340

I believe that the way to calculate buoyancy is buoyancy force-weight of object= upward force, which is PVg-mg= upward force. If i'm wrong please tell me. I set a target of 147N(15kg) upward force for my project product. Is it that strong? Give me your thoughts.

2. Jul 11, 2012

### CWatters

Maths looks right.

15kG is about the weight of two Bowling balls.

3. Jul 11, 2012

### HallsofIvy

If your "P" is the mass density of water and V is the volume of water of that part of the object below water, then, yes, the bouyancy force is PVg. The total force would be that minus the weight, mg. When the object is "floating", the two must cancel so that the total force is 0, neither up nor down.

As for a target bouyancy of 147 N, what is your question about it? For an icecube that would be much to high. For an ocean liner, it would be much too low!

4. Jul 11, 2012

### Pkruse

I've designed many many buoyant systems for seawater. If figure volume in cubic feet and multiply by 60 lbf per cubic foot. The water is a little heavier than that, but I like the margins in case my material absorbs a little water.