# Air pressure at water depth and buoyancy

I'm doing a project that requires a platform that is able to float up and down a water depth of 0-100m. It'll be pulled down by a fishing line. I'm currently using air as buoyant. This air will be trapped in a container. However there is air pressure at a certain water depth. The air will certainly be compressed at a 100m water depth. What volume of the air should i use? Is it the volume of air needed to float the platform at atmospheric pressure(sea level) or at the 100 water depth.

If i were to use the volume of air to float the platform at 100m, wouldn't the net upward force(buoyancy force against the weight of object) acting on the platform be greater?

## Answers and Replies

Is your container compressible like a balloon or is it rigid?

Yup it's quite rigid.

HallsofIvy
Homework Helper
Then the bouyancy force is the weight of the container minus the weight of the water displaced (the volume of the container times the weight density of water).

LURCH