Air can push !

You're like a fish living at the bottom of the ocean. But you live at the bottom of an ocean of air ! Miles (kilometers) of water are piled up above the fish, and miles of air are piled up above you. All that air is heavy. It has weight. The weight of the air around you presses against you, even though you don't feel it.

Here's how you can tell that air is pressing on things. Fill a drinking glass with water. It must be a glass - a plastic or paper cup won't do. Fill the glass to the very top. Put a piece of stiff cardboard over the top of the glass. The cardboard must cover the whole top.

Now, hold the cardboard in place with your hand and turn the glass upside down. Do this over a sink in case you make a mistake. When the glass is upside down, take your hand off the cardboard.

You may think the water will push the cardboard away and spill out. But this won't happen ! The air beneath the cardboard weighs more than the water in the glass. So the air holds the cardboard in place because it pushes harder against the cardboard than the water does.