How Water Affects Your Buoyancy

There is a principle about water that seems to continue to confuse and mystify modern man. Even though the principle was explained by someone who was born somewhere around 287 BC, the concept of why things float and why they sink continues to vex people. The man was Archimedes. A noted astronomer, inventor, physicist, mathematician and engineer, Archimedes explained that, “any body fully or partially submerged in a fluid is buoyed up by a force equal to the weight of the fluid displaced.” His explanation has withstood the test of time in the scientific circles but those people who know scientists soon realize that when they explain things it can sometimes sound like a foreign language for those listening. We as lay people want an understandable explanation that doesn’t require a slide rule or calculator.

The following is my, keep it simple stupid (KISS), explanation on why things float and why they sink. To give it more relevance and more personalization I am going to use you the reader as the example in my explanation of “Archimedes Principle” on buoyancy.

The first thing that has to be understood is that when you get into a body of water, that body of water is going to have to make room for you. In effect you are pushing the water out of the way when you get in. If you filled a bathtub to the very top with water then get in, the water level will raise enough to make the tub overflow.

If you were to have a Libra Scale big enough for you to be on one side and all the water that you pushed out of the tub one the other it would determine whether you float or you sink. If the water weighs more than you it will hold you up making you more buoyant. If the water weighs less then you will be less buoyant. As a living human being, the simple act of breathing in and breathing out while you are in the water will have an effect of floating and sinking. When you inhale you will be occupying more space in the water and when you exhale you will occupy less space.

If you ask someone to write a list of common things that sink in water, you might see items made of metals like steel and items made of rock or concrete. Since the inanimate objects on the list do not breathe then their buoyancy would seem to be fixed. We could logically assume that everything made of those materials will sink. This “logical assumption” would be incorrect. If it were true then a steel cruise ship would therefore be impossibility. Though the ship is in fact made of steel, it is how the ship is constructed (the shape) that is the reason that it floats. The rules of Archimedes Principle will still apply.

The difference between the steel objects that are associated with sinking from the list and the steel ship is the shape. One thousand ton steel marble will occupy less space in the water than a 1,000 ton steel ship and even though both objects are made of the same stuff and weigh the same, this steel ship is going to be bigger than the marble by design. The steel ship’s buoyancy will become more negative the minute 1 person steps aboard and will continue to become more negative with the addition of passengers, crew and cargo. Ships can and have sank before but this is usually due to the structure being compromised below the water level.

Another thing that can affect whether an object floats or sinks is the type of water in which it is placed. Salt water is heavier than fresh water. If a bucket filled with salt water and a bucket filled with fresh water were placed on the Libra scale the bucket containing the salt water would definitely outweigh the bucket filled with fresh water. What this means to you is that you float better in the ocean than you do in freshwater lakes. For those wanting to impress their friends, 1 cubit foot of fresh water weighs 62.4 pounds while 1 cubic foot of saltwater weighs 64 pounds. In places such a the Dead Sea and Salt Lake is Salt Lake City, Utah, the slat water in those areas weighs even more than the salt water found in the oceans.

There are still those people in the world who have trouble staying afloat in salt water. If you are one of those people, fear not, for there are man-made items out there that are designed to help. A snorkeling vest is the way to go, they can be partially inflated with air, which will push more water away from you resulting in additional buoyancy. This writer feels that snorkeling vests should be worn whenever anyone engages in the water. For more information on snorkeling vests and how to select the right one click here. In addition to the vest, another item, which will also help to add to a person’s buoyancy, is a wetsuit.

Wetsuits are made of nitrogen injected neoprene rubber, as this combination, by design is very buoyant. In addition to the buoyancy, they also increase the snorkeler’s ability to retain body heat, which is lost rather rapidly in water and provide protection against accidental contact with marine life.

With all the factors that can affect buoyancy, it is my hope that if you made it this far in reading, then you will have learned a bit more about it. Now go out and impress your friends with your newfound information.