# B Calculating the electrical energy of a buoyant force

1. Jul 25, 2017

### kingsauces

Should be a simple question. Hopefully...

Buoyant object rising in water pulls on a cord attached to a generator. How much power is generated?

Object Volume = 100m2
Liquid is plain water = H2O
Depth = 100m

I understand that Archimedes Principle is the buoyant force = the weight of the displaced water. How do I convert that to KWh?

I am just looking for a very basic estimate. I am not looking to factor in shape, resistance etc ... just need to know if I have a bubble at 100m and I let the sucker go, how much potential energy it would generate.

I tried finding a formula online and it seems like it would be something that someone would create a formula for but my search turned up dry.

Thanks a bunch for any help.

2. Jul 25, 2017

### scottdave

I guess you mean 100 cubic meters for the volume. What is the mass of the object? The net upward force is the vector sum of the buoyant force (up) and the weight (m*g) of the object (down). So this net force will move the object up by 100 meters. You now have work, and if there was no friction you have roughly the potential amount of energy that you can get out. Not exactly, because your "bubble" has a speed, which means it has some kinetic energy.
If it is a bubble shape, you are going to have drag forces, roughly proportional to the square of the speed (if I recall correctly), so make it sort of a missile shape to reduce drag forces.
So you get some amount of energy calculated, then figure out how long it took to rise to the surface, then you could find out the power. But if you plan on getting your submersible back down there, that is going to take some energy.

Just some things to think about.