Liquids press in every direction

A liquid presses down on the bottom of its container. Does it press on the sides too?

Try it (Activity 6.2). Take an old plastic bottle without its cap. With a needle or nail (warm it slightly if it's hard), make four small holes round the sides near the bottom, all at the same height. Cover them with tape, fill the bottle with water, then pull all the tape off at once.

Water squirts out sideways through all four holes, equally. So the water is pushing on the walls, not just the bottom.

A solid only presses down on what it stands on. But a liquid presses in all directions: on the bottom, on the walls, and on everything inside it.

Ever seen water spurt like a fountain from a leaking pipe joint? The water is pressing on the pipe wall, and wherever there's a hole it pushes out.

That's also why a dam is much broader at the bottom than at the top. The water presses sideways on the dam wall and down on the floor. The sideways push is biggest near the bottom, because that's where the column of water above is tallest. A broad base holds the dam up and stands up to that huge push.