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Physics Principles: How balloons float

Updated on September 29, 2012

In General

In simple terms, a balloon floats because the gas used to inflate the balloon, which is usually helium, is light.

A more scientific explanation is that a balloon floats because the gas used to inflate the balloon is less dense than air. In physics, this interaction is called buoyancy. Buoys are those floating things at sear that are used are markers. The term buoyancy was derived from the word buoy because the buoy is able to float using this principle.

The Principle in Balloon floating which is known as buoyancy

The principle behind how buoys and balloons float is called the Archimedes’ principle which is named after Archimedes’ of Syracuse and it states that:

“Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.”

The force acting on a submersed object is called buoyant force. Also, fluid is not only restricted to liquid but anything that flows which includes air. The buoyant force acting on an object is directly proportional to the volume that was submerged and the density of the fluid.


Take for example a balloon that has a volume of 0.005 cubic meters or 5 liters. At standard air pressure at 15˚C, air has a density of 1.225 kilogram per cubic meter. The density of Helium at standard air pressure at 0˚C is 0.1786 kilogram per cubic meter. To compute for the buoyant force, we need to multiply the density of air to the volume of the balloon. We then will get 0.006125 kg of upward force. In newtons that is 0.06006175N.

Since the balloon has its own weight, in order for us to be able to determine if it will float we need to compute for its weight. We have the balloon’s volume and the density of helium. Assuming the weight of the balloon in an un-inflated condition is negligible, we only need to multiply the density of helium which is 0.1786 kilogram per cubic meterto the volume of the balloon which is 0.005 cubic meters. We then will get 0.000893 kilograms. To get the gravitational force acting on the balloon we multiply that by the gravitational constant 9.806 meters per second per second. We then will get 0.008756758 Newtons.

To compute for the upward force acting on the balloon, we simply subtract the weight from the buoyant force. We will then get an upward net force of 0.051305 kilogram-meters per second per second. So, for a balloon with a volume of 0.005 cubic meters or 5 liters filled with helium, the net force is 0.051.


To achieve greater buoyant forces, less dense elements are used. Helium is very “light” because it only has two protons, two neutrons and two electrons compared to oxygen with eight protons, eight electrons and a number of neutrons multiplied by two since it exists in air as a diatomic pair. A more “lighter” element is Hydrogen with only one proton and one electron. However, Hydrogen is unfit for use in the common balloon since it is a very unstable element. It can easily react and ignite.


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    • profile image

      Vishwas Sen 3 years ago

      whether the balloon will burst or not after a certain height? And why?

    • leakeem profile image

      leakeem 3 years ago from Earth

      A balloon will only burst when the outside pressure is too far from the inner pressure such that the balloon expands to a point that the material breaks because of tension. The height differs between balloon materials, atmospheric temperature, and pressure.

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