cause of buoyancy force - the difference between the pressure of the fluid at different depths.Therefore, the Archimedes force appears only in the presence of gravity.On the moon, it will be six times, and on Mars - 2.5 times less than on Earth.

In weightlessness buoyancy force there.If we imagine that the force of gravity in the world suddenly disappeared, all the ships in the seas, oceans and rivers, at the slightest push will go to any depth.But they do not go up will not depending on the gravity surface tension of water, so that they can not fly, all drowned.

## How does the Archimedes force

magnitude of buoyancy force depends on the volume and densi
ty of the submerged body of the medium in which it is located.His exact wording in the modern view: immersion in a liquid or gaseous medium body in the gravitational field acts buoyant force exactly equal to the weight of the displaced body of the medium, ie, F = ρgV, where F - the force of Archimedes;ρ - density of the medium;g - acceleration of free fall;V - volume displaced by the submerged body or a part of the fluid (gas).

If fresh water for each liter of volume of submerged buoyancy body operates in 1 kg (9.81 m), the seawater having a density of 1.025 kg * cu.dm, for the same liter volume will be a force of 1 kg of Archimedes '25 For a man of average complexion difference in strength to support the marine and fresh water will be nearly 1.9 kg.Therefore, swim in the sea is easier: Imagine that you need to cross the pond even without dvuhkilogrammovy flow with a dumbbell in his belt.

on the shape of the body immersed buoyancy force is independent.Take iron cylinder, measure the strength of his expulsion from the water.Then roll the cylinder in a sheet, to plunge into the water, and the flat edge.In all three cases, the Archimedes force will be the same.

strange at first sight, but if immersed flat sheet, the decrease in the pressure difference for a thin sheet offset by an increase in its area, perpendicular to the surface of the water.And when immersed edge - on the contrary, a small area of ​​the rib is offset by the greater height of the sheet.

If the water is very rich in salt, making it the density became higher than the density of the human body, then it will not sink and a man who can not swim.In the Dead Sea in Israel, for example, visitors can lie for hours on the water, not moving.However, to go on it still can not - get a small footprint, a person falls into the water up to his neck, while the weight of the submerged part of the body is equal to the weight of water it displaces.However, if there is a certain amount of fantasy legends about walking on water you can.But in kerosene, the density of which just 0,815 kg * cube.dm, will not be able to stay on the surface and a very experienced swimmer.

## buoyancy force in the dynamics of

That court swim through the power of Archimedes, is known to all.But the fishermen know that the Archimedean force can be used in dynamics.If caught on the hook for big and strong big fish (trout, for example), then slowly pull it to the nets (vyvazhivat) was no use: tear off the line and leave.You must first pull a little when she leaves.Feeling with the hook, the fish, trying to get rid of him, metnet toward the fisherman.Then you need to pull very strongly and sharply, scaffold did not have time to break.

in the water body of the fish weighs almost nothing, but its mass inertia is stored.With this method of fishing buoyancy force as it naddast fish's tail, and production itself plyuhnetsya at the feet of the angler or him into the boat.

## buoyancy force in the air

buoyancy force acts not only in liquids and in gases.Thanks to the flying balloons and airships (zeppelins).1 cu.m air under normal conditions (20 degrees Celsius at sea level) weighs 1.29 kg and 1 kg of helium - 0.21 kg.That is 1 cubic meter of helium-filled envelope is able to lift a load of 1.08 kg.If the shell diameter of 10 m, its volume is 523 cubic meters.m. After completing her from lightweight synthetic material, we get the lift about half a ton.Archimedes force air balloonists called floatable force.

If the balloon pump out of the air, not allowing him to wrinkle, every cubic meter of his pull-up is all of 1.29 kg.The increase more than 20% of the lift force is technically very tempting, but the roads helium and hydrogen explosive.Therefore vacuum airship projects from time to time come to light.However, materials that can withstand a great while (about 1 kg per sq. Cm), the atmospheric pressure on the outside shell, modern technology is not yet able to establish.