Why is it so difficult to breathe when snorkeling at a depth of 1 m, & practically impossible @ depth of 2m?

Question

Why can't a diver simply breathe through a hose that extends to the surface?

Answer 1

if 2m is very deep then it's probably pressure---the deeper you go the more pressure

Answer 2

above water you have to use your diaphragm to fill your lungs with air and this requires that you move the surrounding air (1 atm of pressure) away from your body.  When under water the pressure exerted on your body by the water increases with depth and when you breath, your diaphragm doesn't have the strength to push back on that pressure.

Answer 3

Because the air inside the hose is at atmospheric pressure and water is dense enough that one is trying to expand ones lungs against a much higher pressure of water, especially since the lungs are designed more to compress and blow out and are poor at sucking in against pressure anyway.

Answer 4

I think it has something to do with the pressure around you.  Above the water, around sea level, the pressure exerted on you by the surrounding air is 1atm (approx. 100 kPa).

The equation of pressure in a liquid is P = density*gravity*height.  Density of water is 1000 kg/m^3

At 1m: 1000kg/m^3 * 9.8 m/s^2 * 1m = 9800 Pa, or 9.8 kPa.  That pressure is added to the atmospheric pressure, so instead of 100kPa surrounding you, there's 109.8kPa.  That is almost a 10% increase in the surrounding pressure.

At 2m, the pressure from the water is 19.6 kPa, which means surrounding pressure is 119.6 kPa... a 20% increase in surrounding pressure from above the water.

The increased pressure would make it harder for your lungs to expand, as you would be breathing in air that is at 100 kPa in an environment that is exerting close to 120 kPa on you, and the normal air wouldn't be able to expand the lungs like it would above the water.  That's why you would need pressurized air.  With pressurized air, the lungs would be able to expand as they would above the water.

I apologize if that seems confusing, but I think it makes sense.

I hope it helps.