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Scuba Diving & Buoyancy - Topic Physics Application




One important part of scuba diving is calculating the amount of weight you’ll need to descend and ascend safely during a dive, which can be complicated. An incorrectly weighted dive can be very difficult.

Why is it important that your weight is right during a dive?

Your air consumption will be improved, you’ll have better control of your body and be able to make smooth descents and ascents, you’ll be able to hold your position during safety checks, and you’ll enjoy your dive more.

If you are not correctly weighted, there will be signs during your dive. For instance, your streamlining will be off. Streamlining allows you to maintain a horizontal position in the water. If you are overweighed, your chest will be high and your legs will be below, and you will have to inflate your BCD (buoyancy control device) to compensate. If you're underweighted, your legs will be high in the water and your chest will be low and you will have to continuously kick to keep yourself down.

This problem may be fixed by putting more weight on or taking weights off your belt. You can also adjust the location of your weights to see how it affects your balance. Putting weights in trim pockets could be helpful. If your legs are especially buoyant, ankle weights may come in handy.

There are three levels of buoyancy; positive buoyancy or floating, negative buoyancy or sinking, and neutral buoyancy, or feeling weightless in the water and not sinking. Neutral buoyancy is the goal. Suits cause buoyancy, which needs to be compensated for. Other things that can affect the amount of weight you need include:

  • Your weight and your body mass index (weight vs. height)
  • Whether you’re in saltwater or freshwater
  • The thickness of your suit
  • The weight of your tank and the air in it, because as the air in the tank is consumed, the tank will become lighter and its buoyancy will become positive, causing you to float.

BUOYANCY (Archimedes’ Principle)

A Greek mathematician named Archimedes determined why things float 2000 years ago. He established that "Any object wholly or partly immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object." This explains why a steel ship floats, but its anchor does not. The more water displaced, the greater the buoyancy. If the weight of the displaced water (total displacement) is greater than the weight of the submerged body, the buoyancy is positive and the object floats. If the weight of the displaced water is less than the weight of the object, then the buoyancy is negative and the object sinks. If the weight of the object is equal to the weight of the displaced water, then buoyancy is neutral and the object is suspended. Neutral buoyancy is the state frequently used when diving. Buoyancy is dependent upon the density of the surrounding liquid. Seawater has a density of 64.0 pounds per cubic foot, compared to 62.4 pounds per cubic foot for freshwater. Therefore, each cubic foot of seawater that is displaced by a volume of air in a container has a lifting force of 64 pounds. The greater the density, the greater the buoyancy force. Thus, it is easier to float in seawater than in a freshwater lake 

DIVE TABLE FOR SCUBA DIVING


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