Why Do Helium and Hydrogen Filled Balloons Float in the Air?
Balloons filled with helium or hydrogen seem to defy gravity, floating gently in the air. But what makes them do so?
Archimedes' Principle: The Key to Buoyancy
Archimedes' Principle, discovered by the ancient Greek mathematician and engineer Archimedes, is a fundamental concept that explains the behavior of fluids and gases when objects are partially or fully submerged in them. Simply put, the principle states that the upward buoyant force (or upward force) exerted on an object is equal to the weight of the fluid (or gas) displaced by the object.
The principle can be expressed mathematically as:
Fb = ρVg
Where:
Fb = Buoyant force
ρ = Density of the fluid (or gas)
V = Volume of the object
g = Acceleration due to gravity
What is Density?
Density is a measure of how tightly packed the molecules of a substance are. It is defined as the mass per unit volume of a substance. In the case of gases, such as helium, hydrogen, and air, their densities are typically measured in units of mass per unit volume (e.g., grams per liter).
The densities of helium, hydrogen, and air are approximately:
Helium: 0.1786 g/l
Hydrogen: 0.0899 g/l
Air: 1.2 g/l
As you can see, helium and hydrogen are significantly less dense than air.
How Does This Relate to Buoyancy?
When a balloon filled with helium or hydrogen is placed in the air, the surrounding air molecules exert a downward force on the balloon, which is equal to the weight of the air displaced by the balloon. Since the balloon is filled with a gas that is less dense than air, the weight of the air displaced is greater than the weight of the gas inside the balloon.
According to Archimedes' Principle, the buoyant force acting on the balloon is equal to the weight of the air displaced. Since the air displaced is greater than the weight of the gas inside the balloon, the buoyant force is greater than the weight of the balloon. This is why the balloon experiences an upward force and floats in the air.
Comparing the Densities
To further illustrate the concept, imagine a helium-filled balloon and a balloon filled with air. If you were to measure the weight of each balloon, you would find that the helium-filled balloon weighs less than the air-filled balloon. This is because the helium inside the balloon is less dense than the air around it.
Conclusion
In conclusion, the reason why helium and hydrogen filled balloons float in the air is due to the principle of buoyancy, as explained by Archimedes' Principle. The density of the gases inside the balloon is significantly less than the density of the air, resulting in an upward buoyant force that causes the balloon to float.