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#### Pressure - Working Model for Phyics

 Posted by The Big Tutor on June 27, 2012 at 10:05 AM

Using Pressure

When the area is small, a moderate force can create a very large pressure. This is why a sharp knife is good at cutting things: when you push the very small area of the sharp blade against something, it creates a really large pressure.

Ice skates have sharp edges, and thus a small area in contact with the ice.

This means that your weight creates a very large pressure on the ice, far more than if you were standing in ordinary shoes.

Ice has an unusual property: it can melt under pressure, even if it's below 0°C. When you're ice skating, you're actually skating on a layer of water that you've just melted, which quickly re-freezes when you move on (you're not skating on ice at all!) This is called regelation, and means that there's very little friction as you skate along.

Even a slender supermodel can damage floors by walking on then in high-heeled shoes. This is because the area of the heel is small, so you can easily create enough pressure to cause a dent in the floor.

The pressure can be greater than if an elephant was standing there, even though the force is much less. So you should be able to figure out why elephants and camels have large feet.

Example:

As you go deeper into a liquid, the pressure increases. You can feel this on your ears as you swim down to the bottom of a swimming pool. We need to remember this when designing the walls of pools and dams: the wall must be thicker at the bottom, to withstand the increased pressure down there.

Categories: Physics

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