Why will a diver become less buoyant as he swims deeper?

Buoyancy of divers

The question is based on an incorrect assumption.

The correct question is "Will a person become less buoyant as he swims deeper? Why or why not?"

The answer is "it depends."

If the person is freediving - yes. His lungs will compress and his volume will decrease while his weight remains constant.

If the person is on SCUBA and assuming no exposure suit and correct weighting, no. On SCUBA, a person's lungs will not compress. His volume will remain the same. As he uses air, the weight of his system will decrease and he and his SCUBA unit will become more (not less) buoyant.

If the person on SCUBA is wearing an exposure suit and/or is overweighted (requiring air in the BC), the suit and/or BC will compress and make the person less buoyant.

Andy's answer is correct within the limits of the situation he describes.

More discussion

Because ambient pressure will increase with depth, decreasing the volume (and thus your bouyancy) of any air pockets present, whether in your BC or your wet suit

Assuming the same volume of air in your BC at 50 feet and at the surface, at 50 feet that air will be compressed into a smaller volume, thus your bouyancy will be less than at the surface.

If you ascend from 50 feet, that air will start to expand, increasing your bouyancy (and thus possibly leading to a runaway ascent)

If you descend from 50 feet, that air will start to compress, decreasing your bouyancy (and thus possibly leading to a runaway descent)

Buoyant force is the upward force on an object. I allows objects to float.

First answer by ID1118940549. Last edit by Waterknife. Contributor trust: 45 [recommend contributor]. Question popularity: 34 [recommend question]