Hot Air Balloon

A hot air balloon is a giant, colourful balloon that floats gracefully in the sky. But have you ever wondered how it stays up despite Earth’s gravity? The hot air balloon was invented in Paris in 1783. Its design includes a fabric envelope to hold hot air, an exhaust at the top, and a basket for passengers. The interesting thing is that it has never changed in centuries.

This article makes it easy to understand hot air balloons, how they work, and the science behind them in detail.

Table of Contents 

• Fun Facts About Hot Air Balloons
• What Is a Hot Air Balloon?
• How Does a Hot Air Balloon Float?
• How Pilots Operate Hot Air Balloons?
• How Buoyancy, Air Pressure, and Gravity Make a Hot Air Balloon Rise?

Fun Facts About Hot Air Balloons

What Is a Hot Air Balloon?

A hot air balloon is a flying aircraft that floats in the air using hot air. In 1783, the Hot air balloon was designed and developed by the Montgolfier brothers, Joseph-Michel and Jacques-Étienne, in Paris(France). A hot air balloon is made up of three main parts:

• The Envelope is the large, colourful balloon that holds hot air

• The burner is the flame that heats the air inside the envelope

• The basket is the part that carries the passengers and the pilot

A hot air balloon floats because the air inside is heated, which has a lower density and becomes lighter than the cooler air outside. Just like a boat is supported by the water in the ocean, a hot air balloon is supported by the cooler air around it.

So, the big question that arises here is: how does science make a hot air balloon float in the sky? Let's discuss 

How Does a Hot Air Balloon Float?

You might have observed how a boat floats on water. Or how a leaf floats on a pond? We already know that the scientific phenomenon behind this is buoyancy.  Hot air balloons float for the Same reason!

But what is buoyancy?

“Buoyancy is the upward force that pushes an object in a fluid (like water or air).”

In a hot air balloon,

• Air acts like a fluid

• Hot air inside the balloon is less dense than the colder air outside

• The colder, heavier air pushes the balloon upward, lifting it off the ground

This principle is called Archimedes’ Principle:

“Any object submerged in a fluid experiences an upward force equal to the weight of the fluid it displaces.”

It can be concluded that,  if something is lighter than the air or water it’s in, it floats!

Here, for a balloon to rise because, 

Buoyant Force > Weight of (Balloon + Air + Passengers)

If the weight is greater, the balloon stays on the ground. If the buoyant force is greater, up it goes! Interesting! 

Now you might be wondering, how does a hot air balloon change direction? Let's discuss, 

How Pilots Operate Hot Air Balloons?

Here’s the funny part about hot air balloons: they don’t have steering wheels or engines. Pilots use their knowledge of wind patterns at different altitudes to move the balloon sideways.

Pilots control only the vertical motion of a balloon:

• To rise, they turn on the burner to heat the air

• To descend, they stop the burner or open a vent at the top to release hot air

Since hot air rises and cold air sinks, the balloon can hover at the perfect altitude when the pilot balances the heat and air release.

The weight of the basket and passengers is at the bottom, while the buoyant force acts from the top. This makes the centre of mass lower than the centre of buoyancy.

But how exactly does a hot air balloon stay stable in the air?

The weight of the basket and passengers is at the bottom, while the buoyant force acts from the top. This makes the centre of mass lower than the centre of buoyancy.

How Buoyancy, Air Pressure, and Gravity Make a Hot Air Balloon Rise?

We already know that Gravity pulls air particles toward the Earth, creating air pressure. At the ground, the pressure is highest. As you rise in altitude, the pressure decreases because there is less air above. 

Air pressure is highest at the surface of Earth because the weight of all the air above pushes down with more gravitational force. As you rise higher into the atmosphere, there is less air above, so the pressure decreases. That’s why air pressure drops as you go up in altitude.

Here, due to the pressure difference, an upward buoyant force is created. However, this buoyant force will be quite weak here. So, for buoyancy to lift an object into the air, the object must be lighter than an equal volume of the surrounding air.

The pressure of air can increase in two ways:

• Adding more air particles makes them hit surfaces more often, increasing the overall pressure.

• When the particles move faster, each hit is stronger and more frequent, also raising the pressure.

In a hot air balloon, heating the air makes the particles move faster, which reduces the air’s density and helps the balloon rise. Because the air inside the balloon is lighter, the cooler, denser outside air pushes it upward, just like water pushes a boat to the surface.

Till now, we have seen that hot air balloons may look magical, but they rise, float, and move because of simple scientific phenomena such as buoyancy, air pressure, gravity, and heat. Once you understand how these forces work together, the floating balloon in the sky makes perfect sense.