A Pessimist would say this glass is half empty, while an optimist would say that same glass is half full.
In the science world, though, scientists would say that glass is full!
The thing about containers is they are full, even when they look empty.
They are full of air molecules.
This air tries to fill every empty space, like the container.
When you pour in a liquid into a container, you are just displacing the air molecules that were in the glass with the liquid, or other substance that is denser.
This means air has weight and air takes up space.
Here is a cool experiment that shows this idea in action.
This pop bottle is full of air, as explained earlier. If you placed a balloon over the mouth of it, no more air can get in, and no air could get out.
If you tried to blow up the balloon, you wouldn’t be able to, because the bottle is already full of air.
If you put a hole in the bottle, though, you can easily blow the balloon up, because the air taking up space is pushed out through the hole, as you add air to the balloon.
The air in the balloon is displacing the air in the bottle through the hole.
Here is where this experiment can get a little weird. Fill that same balloon up.
Once it is inflated, cover the hole with your finger.
You will notice it does not deflate. You can even look inside of it!
The balloon stays full because you filled it with air, and the air molecules in the balloon pushed the air molecules out of the hole.
However, since you are not letting any more air into the bottle, though the hole, the higher pressure in the balloon pushes outward harder than the lower pressure air in the bottle, causing it to stay inflated.
Another way to look at is that the bottle is just staying full of air, even with the balloon inside.
Even when a cup looks empty, it’s actually full of air molecules and science!