Stay Scuba Safe With Buoyancy and Pressure Physics

When you learn to scuba dive one of the things that you study is buoyancy and pressure. This knowledge of some very basic elementary physics is good to have so that you can stay safe when you're scuba diving. Now you don't need to be a scientist, but if you want to keep enjoying the underwater experience then a little knowledge goes a long way toward keeping you safe.

Buoyancy and the Archimedes Principle

When observing things in the water they will either float or sink. Likewise, when you enter the water you too will either float or sink depending on the buoyancy of your body.

Archimede's Principle states that when an object is totally or partially immersed in a fluid it is subject to an upward force equal in magnitude to the weight of fluid it displaces. So it is not the weight of an object that counts because even a loaded aircraft carrier weighing 100,00 tons or a huge ocean liner can float. Objects can float because they displace enough water so that the force pushing up from underneath balances the force of gravity acting down. The same principle applies to people in fresh or salt water.

Here is a question that stumps a lot of beginners. If a diver weighs 200 lbs out of the water, how much does he weigh in the water? The answer is 200 lbs. Your weight is the product of how much mass, m, you have multiplied by the acceleration due to gravity, g. W = mg. You don't have less mass in water and g (near the Earth) is about 32 ft/s^2 or 9.8 m/s^2 in or out of the water.

What's changed in water is that there is an upward directed buoyant force produced by the water underneath you. The water on top pushes downward. The balance of these forces, which is greater, determines whether you'll sink or float. When you float you are said to have positive buoyancy and when you sink then you have negative buoyancy. If you're stationary you have neutral buoyancy.

Air is less dense than water and so it floats. The air in your lungs tends to make you positively buoyant. That upward force is counteracted by the weight of your body, the buoyancy compensator (a jacket containing weights with a means of holding the tank) and the other gear you carry. The numbers depend on your specific weight, the gear you are using and the kind of water you dive in. Salt water is denser and heavier, so you have to displace less of it in order to be positively buoyant.

Pressure

A column of air as tall as the atmosphere would weigh about 14.7 lbs (6.7 kg). Thus, the air pressure per square inch acting on your head and shoulders is about 14.7 lbs per square inch. Water exerts a much greater force because it is much denser and heavier. It only takes a column of water 33 feet (10m) high to weigh 14.7 lbs. Thus, the water pressure at a depth of 33 feet is 2 atm. (1 atm from the air + 1 atm from the water. atm = atmosphere, a unit of pressure.) That pressure on your body increases as you go deeper underwater so that at 66 feet you experience 3 atm, at 99 feet 4 atm, and so forth. One thing to keep in mind is that the gauge pressure that is shown on a depth gauge will discount the 1 atm from the atmosphere.

Now you have a basic understanding of some of the physics involved in scuba diving. With this little bit of physics under your diving belt, you're ready to learn about the fluids that pertain to both water and gases and how they affect you under the water.

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About The Author:

HG is a successful author and regular contributor to http://www.sun-and-surf-scuba-diving.com. Buoyancy and Pressure