How to Prove Air Has Volume

Air, and how it behaves and moves, is important to understand the basic processes that lead to weather. But because air (and the atmosphere) is invisible, it can be hard to think of it as having properties like mass, volume, and pressure — or even being there at all!

These simple activities and demos will help you prove that air indeed has volume (or in simpler terms, takes up space).

Activity 1: Underwater Air Bubbles

Materials:

• A small (5-gallon) fish tank or another large container
• A juice or shot glass
• Tap water

Procedure:

1. Fill the tank or large container about 2/3 full of water. Invert the drinking glass and push it straight down into the water.
2. Ask, What do you see inside the glass? (Answer: water, and air trapped at the top)
3. Now, slightly tip the glass to allow a bubble of air to escape and float to the surface of the water.
4. Ask, Why does this happen? (Answer: The air bubbles prove there is air that has volume within the glass. The air, as it moves out of the glass, is replaced by the water proving air takes up space.)

Activity 2: Air Balloons

Materials:

• A deflated balloon
• A 1-liter soda bottle (with label removed)

Procedure:

1. Lower the deflated balloon into the neck of the bottle. Stretch the open end of the balloon over the mouth of the bottle.
2. Ask, What do you think will happen to the balloon if you tried to inflate it like this (inside the bottle)? Will the balloon inflate until it presses against the sides of the bottle? Will it pop?
3. Next, put your mouth on the bottle and try to blow up the balloon.
4. Discuss why the balloon does nothing. (Answer: To start with, the bottle was full of air. Since air takes up space, you're unable to blow up the balloon because the air trapped inside the bottle keeps it from inflating.)

Alternate Example

Another very simple way to demonstrate that air takes up space? Take a balloon or brown paper lunch bag. Ask: What's inside of it? Then blow into the bag and hold your hand tight around the top of it. Ask: What's in the bag now? (Answer: air)

Conclusions

Air is made up of a variety of gases. And although you can't see it, the above activities have helped us prove that it has weight, albeit not much weight — air just isn't very dense. Anything with a weight also has mass, and by the laws of physics, when something has mass it also takes up space. 

Source

Teach Engineering: Curriculum for K-12 Teachers. Air – Is It Really There?