The States of Buoyancy

Video

Key Points

You most likely remember reading about the Greek mathematician Archimedes in school. Archimedes discovered that an object, wholly or partially immersed in water, is buoyed up by a force equal to the weight of the water it displaces. We call this Archimedes Principle. As divers, we’re chiefly concerned with the three states of buoyancy: positive, negative and neutral

• Positive Buoyancy: Objects that weight less than the water they displace float, and are said to be positively buoyant. As a diver, it helps to be positively buoyant when resting or swimming on the surface.

• Negative Buoyancy:Objects that weight more than the water they displace sink, and are said to be negatively buoyant. Being slightly negative helps at the beginning of a descent, so that you don’t have to struggle to get down.
• Neutral Buoyancy:Objects that weigh exactly the same as the water they displace neither float nor sink, and are said to be neutrally buoyant. Under water, this is the ideal state for divers to be in. It allows us to hover motionless. It makes swimming easier. Over all, it makes diving safer and more enjoyable. Equally important, it helps us avoid contact with the bottom, and thus helps protect the fragile aquatic environment.

In the section on Equipment, we’ll discuss the items you will use to help control your buoyancy. In the section on Diving Skills, we’ll examine techniques such as proper weighting, BC use and breath control, which you will use to fine tune your buoyancy under water.

Fresh Versus Salt: Because salt water contains more dissolved minerals, it weighs more than an equal volume of fresh water. This is why objects are more buoyant in salt water — and why you need to wear more weight in salt water than you would if diving the same equipment in fresh water.

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