LAW OF FLOTATION

A body will float in a liquid, if the weight of the body is equal to the weight of the liquid displaced by the immersed part of the body.

The Three Laws of Floatation:

1. Density of the material of the body is less than or equal to the density of the liquid.

2. If density of material of body is equal to density of liquid, the body floats fully submerged in liquid in neutral equilibrium.

3.When a body is in neutral form of equilibrium, the weight of the body is equal to the weight of displaced liquid

Conditions for an Object to Float

• The fluid in which the object has to float should have a density more than that of the average density of the floating object.
• The total weight of the object must be equal to the upthrust force of the fluid on the object.
• To displace a huge amount of fluid, the volume of the object submerged must be huge enough.

Relationship between Real Weight of a Floating Body and Upthrust

As we know,

Real weight = apparent loss in weight + apparent weight

Where apparent loss in weight is equal to the weight of the fluid displaced, which is the upthrust

Therefore

Real weight = upthrust + apparent weight

But, the apparent weight of an object becomes zero when it floats.

Hence, apparent weight = 0

Now,

Real weight = upthrust + 0

Therefore, real weight = upthrust.

Daily Life Applications of the Law of Floatation

• In waterways transportation

The law of floatation is applicable to all the containers that travel by waterways, consisting of ships, boats and submarines.

• In transportation by airways

Hot air balloons and airships are the most widely used air transport mediums that use the law of floatation.

• In decoration

Balloons filled with lighter gases used for decorative purposes also work on the law of floatation.

• In the measurement of specific gravity of liquids

To measure the specific gravity of liquids, an instrument is used, which is named hydrometer. It employs the law of floatation.

How does a submarine sink and float?

A ship that can travel deep underwater as well as on the surface too is known as a submarine. Using the law of floatation, the submarine owes its ability to dive and come up to the surface of the water. It holds weight tanks on either side, which are occupied with water when it has to dive into the waters and are emptied when it has to come up. The tanks are filled and emptied using the special pumps.

How does a hot air balloon float?

A hot air balloon comprises three parts, the burner, the balloon, and the basket. Propane gas is used by the burner to heat up the air in the balloon, and as soon as the air in the balloon gets hot, it enlarges or expands, which results in the rise of a balloon because its density becomes lower than the surrounding air.

To get the balloon down, the pilot can open a parachute valve at the top of the balloon, which decreases the temperature and density inside the balloon because it causes cold air to enter the balloon. Also, by burning less fuel, the pilot can let the air inside the balloon cool itself.

How does an Airship Float?

The airship floats in the sky using the helium and hydrogen gases because these gases are lighter, and they help the airship to rise up; by means of a propeller attached to the ship, manoeuvrings are done. The engine is used to propel the ship, and the lighter gas gives it a lift.