Question

1) A scuba diver swims below the surface, breathing air from tanks of her scuba gear.

a. It’s easiest for her to maintain a constant depth if the buoyant force on her and her equipment exactly balances their weight. How should her average density compare with that of the water around her?

b. When she is 20 m below the surface of the water, what is the pressure pushing inward on her chest?

c. When she breathes, she expects air to flow into her lungs. What is special about the air in the tank and why does it needs to be regulated?

d. If instead of taking with her, some divers use an airline from the surface. What are issues with atmospheric pressure and the supply line she is using?

2) When a patient receives an injection, fluid passes from a cylinder with a plunger in it, through a narrow, hollow needle, and into the patient’s arm.

a. Why will fluid travel more rapidly through the needle if the nurse squeezes harder on the plunger?

b. As the fluid flows out of the needle and slows down in the patient’s tissue, what happens to its pressure?

c. Why doesn’t the blood flow back out of the vein when the needle is removed?

3) A traditional water cooler has a large bottle of water turned upside down so that its neck is submerged in a small chilled water reservoir at the top of the water cooler. The water level in the small reservoir remains just above the neck of the bottle. If you open the valve to let water out of the reservoir, bubbles of air rise up into the water bottle and the level of water in the bottle goes down.

a. Since there is no true seal between the neck of the bottle and the reservoir, what holds the water up inside the water bottle?

Answer 1

1)

(a) Her density should be exactly equal to the density of the water around her.

(b) About 3 times atmospheric pressure (300,000 Pa).

(c) The pressure in her mouth must be greater than the pressure in her lungs. For stationary air to begin flowing into the diver's lungs, the pressure in her lungs must be lower than that in her mouth.

(d) Air will flow out of her lungs and into the airline. When she tries to breathe through it, the pressure in her mouth will be atmospheric pressure and the pressure in and around her lungs will be much greater. Air will accelerate toward her lungs and she will breathe out rather than in.