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What is pressure?

A nail being hammered into wood.A nail being hammered into wood.Pressure is the force exerted by something over a certain area. A nail goes into wood easily because the force hammering it in is concentrated on to the tiny area of the nail's sharp point. This produces high pressure. The same hammer blow might not make a blunt nail enter the wood because the force is spread out over a larger area: the blunt tip of the nail. Because of this, the pressure is lower.

A jacana's long toes spread its weightA jacana's long toes spread its weight

Spreading weight

A jacana, a bird with long toes and claws, can walk over lilypads resting on the water's surface without sinking in. This because its weight is spread over a wide area, so its pressure is low.

Lower air pressure means lower temperaturesLower air pressure means lower temperatures

Air pressure

The lower the air pressure is, the lower the boiling point of water. At sea level, water boils at 100°C (212°F). At the top of Mount Everest, the boiling point drops to 71°C (160°F).

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