When a glass is turned upside down and submerged to 10 m/33 ft, what happens to the air space inside?

At a depth of 10 meters (or 33 feet), the pressure of the water exerts an increase on the air space inside the glass. Under water, the pressure increases by approximately 1 atmosphere for every 10 meters of depth. This additional pressure affects the volume of air contained within the glass due to Boyle’s Law, which states that the volume of a gas is inversely proportional to the pressure exerted on it when temperature remains constant.

As the glass is submerged, the increased external pressure compresses the air inside, reducing its volume. Specifically, at 10 meters, the pressure is around 2 atmospheres (1 atmosphere of air pressure at the surface plus 1 atmosphere from the water column). This pressure effectively leads to a reduction in the size of the air space to about half of its original volume.

This is why the air space becomes half the size when the glass is submerged to this depth, reflecting a basic principle of physics that is essential for divers to understand regarding buoyancy and the behavior of gases under pressure.