Balloons moving up in the air always fascinate us as children. But have you wonder why they move up in the air?
The underlying principal for balloons upward movement is the same as that of objects floating on water.
The balloon moves in the upward direction due to difference in the densities of the balloon and the air.
The balloons which move up in the air are usually filled with some light gas such as Helium whereas air is a mixture of several different gases and hence it has much higher density as compare to Helium.
When the Helium-filled balloon is released in the air, it experiences a force in upward direction which is known as buoyant force. This is due to the fact that the density of air is higher as compare to the density of balloon filled with Helium.
The strength of the buoyant force is equal to the weight of the air displaced by the balloon.
As the weight of the Helium-filled balloon is less than the buoyant force, hence the balloon moves up in the air.
In other words, as the upward buoyant force is greater than the weight of the Helium-filled balloon, therefore the balloon moves up in the air.
Archimedes principle
The principal which explains the upward buoyant force is known as Archimedes principle. It states that a body completely or partially submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces. This principle was named after Greek mathematician and engineer Archimedes who first discovered this principle.