The Physics of Scuba Diving

Genral Information

Physics 24 Web Project
April 11, 2004
Group Members: Lucy Guill, Lindsy Masters, Lee Tennille, David Kleisch


Purpose: To demonstrate the importance and reveal the interesting aspects of the physics principles of pressure and buoyancy in the sport of scuba diving.

Pressure:

The pressure exerted by a fluid is defined as the magnitude of the force acting perpendicular to a surface divided by the area over which the force acts. Pressure can be created by all fluids that have mass, including water and air. Less water than air is required to create an equal pressure because of water’s greater density.

Density:

The mass density is the mass of a substance divided by its volume.

The denisity of air is 1.29 kg/m3. The density of fresh water is 1000kg/m3. The density of salt water is 1027 kg/m3 because it contains salt, giving it a greater mass/unit of volume.

At sea level we experience 14.7 pounds of pressure per square inch (psi). This pressure is equivalent to 1 atmosphere of pressure (1 atm). In fresh water, a diver would experience a pressure of 2 atm at 33 feet or 10.3 m. This change is pressure greatly complication a human’s process of breathing.


Sample Calculation:

Final Pressure = Initial Pressure + (density of fresh water)(acceleration due to gravity)(depth) =

2 atm(1.013e5 Pa/atm) = 1atm(Pa/atm) + (1000kg/m3)(9.8m/s2)(h)

h = 10.3 meters

When under water, the air in a diver’s lungs is being compressed by the pressure of the water above the diver. The volume of the diver’s lungs, therefore, becomes smaller, but the amount of air required by the body and needed in each breath remains constant. For this reason, the air that a diver breaths in must be at the same pressure as the body of the diver.

A diver would not be able to breathe through a hose that provides air from the surface because this air would have a large volume, and the human lung would have to be capable of pushing the weight of water outward to provide a greater volume in the lungs for this air.

For these reasons, it is necessary to use pressurized air tanks while scuba diving. These tanks contain a mixture of gases including oxygen that is pressurized to match the pressure that the diver experiences.

Buoyancy:

Any fluid applies a buoyant force to an object that is partially or completely immersed in it; the magnitude of the buoyant force equals the weight of the fluid that the object displaces:
Magnitude of buoyant force (Fb) = Weight of displaced fluid (Wfluid)

• 3 States of Buoyancy
1. Positive - If an object displaces an amount of water weighing more than its own weight
2. Neutral - If an object displaces an amount of water weighing equal to its own weight
3. Negative - If an object displaces an amount of water weighing less than its own weight

A buoyancy compensator is used by divers for changes in buoyancy. Before beginning a dive, divers let all the air out of the buoyancy compensator, and then gradually add air as they continue downward in order to maintain a neutral buoyancy. This state is essential in scuba diving because a diver must ensure that they do not float upward nor fall too quickly downward. By exhaling a diver looses pounds of buoyancy.