# Background Essay

Scuba diving is an activity that can be both educational and enjoyable. When thinking about scuba diving, most people only think about the pleasures that it offers. Usually, people do not realize how educational scuba diving can be. Boyle's Law is a law that all scuba divers should know before they begin diving. Boyle's Law relates the volume of all gasses to the pressure exerted on all gasses inversely. This means that the volume of the gas increases, the pressure exerted on that gas decreases, and as the volume of a gas decreases, the pressure exerted on that gas increases. Boyle's law is a key aspect to take into account while scuba diving. Robert Boyle, an Irish-born English scientist, was born in 1627. His formula, P1xV1=P2xV2 (original pressure x original volume =present pressure x present volume), is very useful to know as a scuba diver.
First, let's take a look at what happens to divers as they go to different depths without scuba gear. The diver has to take a deep breath at the surface, and as the diver dives to a depth of thirty-three feet, with two atmospheres of pressure on the diver, the air inside the lungs would have decreased by one half. When you have three atmospheres of pressure on you, the air in your lungs decreases to one third of its original volume. Then as the diver comes back to the surface, the air in the lungs will expand again to the original volume if you have not exhaled at all as you ascend.
Now let's take a look at the effects of Boyle's law on divers aided by scuba gear. When you breathe air from a scuba tank under water filling your lungs half way full at a depth of three atmospheres (66 feet under the surface) and then come up to the surface with out breathing out any air, the air will expand in your lungs by three times. Also, even if you have recently exhaled and you are pretty deep under water, since you can never completely empty your lungs, you will have to keep on exhaling as you come up to the surface. Boyle's law explains why you have to exhale as you surface and not hold your breath while breathing from a tank because the volume of the gas inside your lungs changes as the pressure at which this gas is put in changes. For every atmosphere, or thirty-three feet, you go deeper into the water, the pressure increases by 14.7 PSI (pounds per square inch.) If we take a breath at the surface, and then go down to two atmospheres of pressure, 33 feet below the surface, the volume of the air would decrease by one half. Then as you go to three atmospheres below the surface, the volume of the gas would be one third of the original pressure. The formula that represents this is P1xV1=P2xV2. When you have three atmospheres of pressure on you, and have more than one third of your lungs full of air, you have to exhale as you surface in order for your lungs not to burst. Although you will still survive if you have less than one third of your lungs full at sixty-six feet deep, you should exhale anyway as you surface just to be safe. If you take a breath to fill your lungs completely at two atmospheres deep, you will have to exhale as you surface because the volume of the air in your lungs increases as you come up.

The work of Robert Boyle is very important to know about as you scuba dive. Volume of a gas and pressure exerted on a gas vary inversely. You need to always exhale as you come up to the surface from under water to prevent the gas expansion giving lung damage.