Height of water

The idea

The pressure exerted by a liquid increases with the height of its column and does not depend on the amount of liquid.

Overhead tank

A water tank on a roof is placed up high, not on the ground.

Why is it placed at a height?

• The higher the water column, the greater the pressure at the tap
• A tall tank is easier to fill
• It keeps the water cooler

Balloon at the bottom

Open each tab. Watch how much the balloon bulges.

Height matters

When the water column is taller, the pressure at the bottom is greater. The two pipes of different widths held different weights of water, yet the balloons bulged equally. So the pressure depends on the height of the column, not on the amount of liquid.

The pressure of a liquid increases with the height of its column. It does not depend on the amount of liquid.

• Water column | Balloon bulge
• Short | Small
• Tall | Big
• Wide pipe, same height as a narrow pipe | Same as the narrow pipe

Notes

Liquid pressure increases with the height of the column. It does not depend on the amount of liquid.

Check yourself

The pressure at the bottom of a liquid column grows when the …

A narrow pipe and a wide pipe hold water to the same height. Their balloons bulge …

Overhead tanks are placed at a height so that the pressure in the taps …

Does the pressure of a liquid depend on the amount of liquid in the vessel?

• height of the column grows — correct. Yes!
• pipe becomes narrower. Width does not decide the pressure. Height does.
• pipe becomes shorter. A shorter column gives less pressure.
• more in the wide pipe. The wide pipe holds more water, but the pressure depends on height, so the bulge is the same.
• the same — correct. Yes!
• more in the narrow pipe. The narrow pipe holds less water, but the pressure depends on height, so the bulge is the same.
• is decreased. A greater height gives a greater pressure.
• does not change. Height changes the pressure.
• is increased — correct. Yes!
• No, it depends on the height of the column — correct. Yes!
• Yes, more liquid always means more pressure. Equal heights gave equal bulges even though the weights were different.
• Yes, it depends only on the colour. Colour has no effect. Height of the column matters.