The Physics of Airships and Hot Air Balloons

Both airships and hot air balloons fly by utilizing the principle of being lighter than air.

Instead of generating lift with wings like an airplane,

they float in the sky using "buoyancy."

This buoyancy is a principle discovered by the

ancient Greek scientist,
Archimedes.
An object receives an upward force

equal to the weight of the fluid it displaces.

Since air is also a fluid,

buoyancy acts even in the air.

In other words,

if you are lighter than the surrounding air,

you will naturally float upward.

Hot air balloons use heat to become lighter

A hot air balloon

heats the air inside with a burner.

As the temperature rises,

the air expands.

Because the amount of air within the same volume decreases,

the density becomes lower.

Then,

it becomes lighter than the surrounding cold air,

and the buoyancy overcomes gravity, causing it to rise.

Conversely,

when the burner is turned down, the air cools,

the density increases, and it descends.

In short,

it is a vehicle that uses temperature to adjust its buoyancy.

Airships use lighter gases

An airship

contains a very light gas inside.

What is mainly used today is

helium.

In the past,

hydrogen

was also used.

Hydrogen is even lighter,

allowing for greater buoyancy.

However, because it is extremely flammable,

the safer helium is the mainstream choice today.

Airships can be steered

Hot air balloons are basically at the mercy of the wind.

On the other hand,

airships have

propellers and engines.

They can move forward, backward, left, and right,

and their direction can be changed using a rudder.

In other words,

an airship is

a "floating ship."

How much buoyancy is there?

Buoyancy is determined by

the weight of the displaced air.

For example,

if you displace 1,000 cubic meters of air,

it amounts to nearly 1.2 tons of air weight.

Subtracting the weight of the

balloon or airship itself,

and the weight of the internal air or helium,

the remainder is the force available to carry people and cargo.

Therefore,

the larger the airship,

the heavier the cargo it can carry.

Why are they so huge?

Airships look very large.

This is because

buoyancy is proportional to volume.

The more air you displace,

the greater the buoyancy you obtain.

Therefore,

to carry heavy cargo,

a massive hull is required.

Differences from airplanes

Airplanes

generate lift on their wings by moving forward.

If they stop,

the lift is lost.

However,

airships and balloons

have buoyancy even when stationary,

so they can remain in the air.

This is the biggest difference.

Summary

Airships and hot air balloons

both fly by utilizing the fact that they are lighter than air.

Hot air balloons make the air lighter with heat,

and airships use light gases like helium.

And,

what supports both of them

is the principle of buoyancy discovered by Archimedes about 2,200 years ago.

When we look up at the sky,

the sight of an airship moving slowly or

a balloon rising quietly

is governed by simple and beautiful physical laws.