Why is helium used in balloons and airships?

Helium is used in balloons and airships because it is lighter than air and non-flammable.

Helium is a noble gas, which means it is chemically inert and does not react with other elements or compounds. This makes it safe to use in balloons and airships as it will not combust or explode, unlike hydrogen, which was used in airships in the past with disastrous results.

The primary reason helium is used, however, is due to its low density. Helium is lighter than air, which means that a balloon filled with helium will float. This is due to the principle of buoyancy, which states that an object will float in a fluid if it is less dense than that fluid. In this case, the helium-filled balloon is the object and the air is the fluid.

The helium gas molecules move faster and collide with the balloon's inner surface, creating an upward force known as the buoyant force. This force counteracts the force of gravity pulling down on the balloon, causing it to float in the air.

In airships, the use of helium allows them to control their altitude by adjusting the amount of helium in their gas bags. If the airship needs to ascend, more helium is pumped into the gas bags, making the airship less dense than the surrounding air. To descend, some helium is released, increasing the airship's density.

In summary, helium's non-reactive nature and low density make it the ideal gas for use in balloons and airships. Its use ensures safety and provides the necessary buoyancy for these objects to float and navigate through the air.