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Helium is safer when used on hot air balloon although it offers marginally less lifting power. Helium is used for purposes that require some of its unique properties, such as its low boiling point, low density, low solubility, high thermal conductivity, or inertness. Pressurized helium is commercially available in large quantities.

Because it is lighter than air, airships and balloons are inflated with helium for lift. In airships, helium is preferred over hydrogen because it is not flammable and has 92.64% of the lifting power of the alternative hydrogen.

In physics, buoyancy is the upward force on an object produced by the surrounding fluid (i.e., a liquid or a gas) in which it is fully or partially immersed, due to the pressure difference of the fluid between the top and bottom of the object. The net upward buoyancy force is equal to the magnitude of the weight of fluid displaced by the body. This force enables the object to float or at least to appear lighter. Buoyancy is important for many vehicles such as boats, ships, balloons, and airships.

The ancient Greek scientist, Archimedes of Syracuse, first discovered the law of upthrust, hence it is sometimes called Archimedes' principle: Hiero the second asked Archimedes if he could find out if the gold crown he has gotten from the goldsmith was pure gold. Archimedes knew that all he has to do was determine whether the density of the crown matched the density of gold.Archimedes measured the mass easily with a balance. He later found out how to get the volume of the crown while in the sauna. A solid can displace water out of a container. To find the volume all he had to do was measure the volume that came out of the container when he put the gold crown in. Thus he found out the goldsmith had tried to cheat the king with a mixture of gold and silver for his crown

The upthrust is equal to the weight of the displaced fluid.
The weight of the displaced fluid is directly proportional to the volume of the displaced fluid (specifically if the surrounding fluid is of uniform density). Thus, among objects with equal masses, the one with greater volume has greater buoyancy.

Suppose a rock's weight is measured as 10 newtons when suspended by a string in a vacuum. Suppose that when the rock is lowered by the string into water, it displaces water of weight 3 newtons. The force it then exerts on the string from which it hangs will be 10 newtons minus the 3 newtons of buoyant force: 10 − 3 = 7 newtons. This same principle even reduces the apparent weight of objects that have sunk completely to the sea floor, such as the sunken battleship USS Arizona at Pearl Harbor, Hawaii.

The density of the immersed object relative to the density of the fluid is easily calculated without measuring any volumes:

If the weight of an object is less than the weight of the fluid the object would displace if it were fully submerged, then the object has an average density less than the fluid and has a buoyancy greater than its weight. If the fluid has a surface, such as water in a lake or the sea, the object will float at a level so it displaces the same weight of fluid as the weight of the object. If the object is immersed in the fluid, such as a submerged submarine or a balloon in the air, it will tend to rise.

If the object has exactly the same density as the liquid, then its buoyancy equals its weight. It will tend neither to sink nor float.

An object with a higher average density than the fluid has less buoyancy than weight and it will sink.

A ship floats because although it is made of steel which is more dense than water, it encloses a volume of air and the resulting shape has an average density less than that of the water.

1 I think there are two reasons
First Helium is extremely light
Its density is lower than air
Besides that Helium is stable
In the period table It is in group 0
This means it is not explosive
It is safety that we use Helium balloon

2 This is because Hydrogrn is explosive
and not stable
It occurs accidents easily

1 I think there are two reasons
First Helium is extremely light
Its density is lower than air
Besides that Helium is stable
In the period table It is in group 0
This means it is not explosive
It is safety that we use Helium balloon
2 This is because Hydrogrn is explosive
and not stable
It occurs accidents easily