Swimming and floating, density, the ability to float depends on your body being less or equal to that of water

Swimming and floating /Flotation and density

When swimming and floating, there are very few people who cannot swim. The ability of the human body to float depends upon it having a density less than or equal to that of water, which is one.

DENSITY=MASS=grammes Volume cc


Air 0.0129 Fat 0.94

Human body 0.98 (approx)

Water (fresh) 1.00 Water (salt) 1.026

Muscle 1.058 Skin 1.10 Hair 1.30 Bones 1.38 Teeth 2.24

The human body is made up of various components, each with differing densities, but floats overall, because it's density is less than ONE. The human body is also different from other objects which floats in water because the human body is FLEXIBLE.

Swimming and floating /floatation

The weight of the body (which is the downwards thrust of gravity), pulls the body downwards. When the body is immersed in the water, or any other liquid, the liquid pushes up against the body. This is called upthrust, and can be easily demonstrated by first weighing an object in the air, and then immersed in liquid. The apparent weight of the object is less. The depth of the water has no bearing on it's capacity to support a floating body. (a fact which can be particularly re-assuring to those who have a fear of deep water as well as those who feel they will sink to the bottom of the pool).

When the body is immersed in a liquid, the liquid will be displaced by the immersed body. This liquid will have the weight of the body.

UPTHRUST=The weight of the liquid=the weight of the body

Swimming and floating /buoyancy

Buoyancy in the water will be determined by the body mass, body fat and the amount of air in the lungs. The person carrying more body fat will float high in the water, whilst the person not carrying as much body fat will tend to float vertically with the legs and hips well under the surface.

Swimming and floating /Buoyancy and gravity

Let's look at the mushroom float, this is also called a tuck float, tucking arms and legs tucked to your chest. Head tucked in and arms over the knees making yourself into a ball. Whilst doing this mushroom float there are two forces which acts upon the body:-

1) the pull of gravity, which acts through the center of gravity

2) the upthrust of the water, acting at the centre of the upright position, these two forces, acting in opposition, are not necessarily in line. However, as the body rotates, or rocks, with the face in the water and knees tucked under the chest, a position of equilibrium becomes reached, and movement ceases. The two forces are now acting along the same vertical line.


Laws of motion and matters (Newton's laws)


Every object continues in its state of rest, or of uniform motion in a straight line, except so far as it is compelled to change that state by external forces.


The rate of change of the momentum (mass x velocity) is proportional to the impressed force and takes place in the direction in which that force acts.


ACTION AND REACTION ARE EQUAL AND OPPOSITE (Every action i.e. swimming have an equal and opposite reaction).

Swimming and floating/ transfer of momentum

The momentum in one mass (energy) is passed onto another. For example a red snooker ball being struck by a white ball

Bernoulli's principle (simplified)

Pressure difference created by a wing travelling at speed, so creating lift.

Swimming and floating /click here to return to home page

Hope you have enjoyed this page, thanks for reading.

Dale Dudley

Thanks for visiting the first page, one of two .The next page discusses the propeller theory in terms of swimming and some of the laws/principles, and it's relation to the four strokes. Click here to go onto my second page on the laws/principles of swimming