Although we don’t think about it very much, air is something very important. We need to breathe it to stay alive, it is part of what creates our weather here on Earth, and it allows birds and air planes to fly. Because air is everywhere around us and above us, and we can move and see through it so easily, we tend to think of air as being “light”. But is this really true? Is air light, or does it have weight like any other object?
First, we need to discuss, what exactly is air? Air is a mixture of different gaseous elements (that is, building blocks) which, because of Earth’s gravity, surround the planet like a blanket. These gasses are also referred to as Earth’s “atmosphere”, which extends from the surface of the Earth to halfway to the moon (over 440 miles).
Next, we need to discuss what weight is. When we say an object “weighs” a certain amount, it means the Earth’s gravity is pulling down on it with a certain force. For instance, if we say a bag of flour weighs 5 pounds, this means that the Earth is pulling that bag of flour towards itself with a force of 5 pounds. Therefore, anything under the influence of the Earth’s gravity (that is, anything the Earth is pulling down on) is going to have some weight.
But wait...if gravity is keeping the atmosphere—the air—in place, that means Earth is pulling down on it! If Earth is pulling on it, the way it does other objects, that means it has weight like other objects! So we can now say yes, air has some weight! But how much does air actually weigh? That depends on how high up we go.
As we measure the weight of the air (also called the atmospheric pressure) farther away from the Earth’s surface, gravity pulls the air down with less and less force, so air actually weighs less the farther away we are from Earth. Often we use the Earth’s “sea level” (that is, the average weight of the ocean) as a standard for elevation, and at sea level the air will weigh 1.2 kg/m3, or about 2.6 pounds per cubic meter. That means that if you could make a square box that was about three feet long on every side, the air inside that box would weigh about 2.6 pounds at sea level. It also means that if you had a column of air as high as the Empire State Building in New York City (443.2 meters high), it would weigh over 1,000 pounds!
So now we know that air is actually pretty heavy. But back to our original question, is anything lighter than air? The answer is yes! Since air is made up of certain elements (mostly nitrogen and oxygen), any gaseous elements or molecules that are lighter than these elements—such as helium, hydrogen, or methane—will be “lighter than air”. This is why when you fill a balloon with helium, it floats!
TRY THIS!!
To prove to your friends that air has weight, try this experiment!
TRY THIS!!
To prove to your friends that air has weight, try this experiment!
Here’s what you need:
1. Two latex balloons
2. A pencil or a wooden dowel
3. Three pieces of string or thread, one about two feet long, and the other two six inches each
4. Strong tape, such as duct tape
First, blow up one of the balloons. Get a parent or teacher to help you if you have trouble!
Next, tie the pencil or dowel to the two-foot piece of string such that it balances straight across—one end should not be higher than the other. Fasten the other end to the top of a door with strong tape, such that it hangs suspended in the doorway. Get a parent or teacher to help you with this, too!
1. Two latex balloons
2. A pencil or a wooden dowel
3. Three pieces of string or thread, one about two feet long, and the other two six inches each
4. Strong tape, such as duct tape
First, blow up one of the balloons. Get a parent or teacher to help you if you have trouble!
Next, tie the pencil or dowel to the two-foot piece of string such that it balances straight across—one end should not be higher than the other. Fasten the other end to the top of a door with strong tape, such that it hangs suspended in the doorway. Get a parent or teacher to help you with this, too!
Tie the empty balloon to one end of the pencil or dowel using one of the six inch pieces of string, and tie the air-filled balloon to the other end of the pencil or dowel using the other piece of string. Watch what happens!
REMEMBER: If the air has weight, the balloon with the air will be heavier than the balloon without air. As such, it will pull down on the end of the dowel or pencil which it is tied to.
REMEMBER: If the air has weight, the balloon with the air will be heavier than the balloon without air. As such, it will pull down on the end of the dowel or pencil which it is tied to.
What happened when you tied the full balloon and empty balloon to the pencil? Write down what you saw.
