force is a push or a pull on an object and is measured in Newtons (N).

Pressure is caused when a force is applied over an area.

 

Hitting a nail into a wall puts the point of the nail under high pressure. You have used the hammer to provide a large force. The sharp point of the nail concentrates the force over a very small area so the nail can move through the wall.

 

 

Some vehicles, like tanks, are fitted with caterpillar tracks. This lets them spread their weight out over a larger area and stops them getting bogged down. Tractors have wide tyres for the same reason, to spread the weight out and lower the pressure.

 

Sharks are very good predators and have been for millions of years. They have very strong jaws and their teeth are very sharp. Because their teeth are so sharp, sharks can concentrate all the force from their jaws into a small area at the tips of their teeth. This high pressure lets them tear flesh.

 

Snowboards rely on pressure too. The snowboard is designed not to sink into the snow. The board spreads the weight of the person out over a larger area and this keeps the pressure low. Camels can walk on sand because they have large feet that spread their weight out, lowering the pressure.

 

Q1: Why does a nail have a sharp point?

A1: To concentrate the force applied by a hammer onto a small surface area. This concentration of the applied force allows a nail to penetrate a wall.

 

Q2: Why is it useful for tanks to have caterpillar tracks?

A2: So that their weight can be spread out over a larger surface area. This prevents them from sinking into marshy ground despite their huge weight. It also gives them greater mobility on the ground.

 

Q3: Why are sharks able to tear through flesh so easily?

A3: Their sharp teeth allow all the force from the jaw to be concentrated over a small area. This puts high pressure on the tips of the teeth and allows them to penetrate and grip their prey.

 

Q4: Explain why a camel is able to walk on sand even when it is carrying a heavy load?

A4: Camels have wide feet which have a large surface area. As the area is large, the pressure is reduced so the camel can avoid sinking into the soft sand.

  

:: High and Low Pressure ::

 

If you keep the size of the force the same then: 
- the pressure is high when the area is small 
- the pressure is low when the area is large

 

Examples of high pressure: Nail, drill bit, screw, ice skates, sewing needle, bread knife...

Examples of low pressure: Tractors tyres, aeroplane wings, building foundations, snow shoes, camel's feet...

 

Q5: Explain what pressure means?

A5: Pressure is the relationship between force and area. (Pressure tells us how the force that is applied and the area over which it is applied are related.)

 

 

:: Calculating Pressure ::

 

Pressure tells us how the force that is applied and the the area over which it is applied are related. An equation is used to work out how much the pressure is.
Or in shorthand:

Because force is measured in newtons (N) and the area is measured in square meters the pressure is measured in newtons per square meters.

Units of pressure are also called pascals (Pa).

1 Pa is exactly the same as 1 N/m2

You can use an area measured in cm2 to calculate pressure but remember that if you do the pressure is calculated in N/cm2.

 

Q6: What is the pressure on the floor when a man of weight 750 N stands on an area of 250 cm2?

A6: Pressure = force / area

= 750 / 250

= 3 N/cm2

 

Q7: Calculate the pressure when a woman of weight 500 N stands in high heels with an area of 1 cm2 each?

A7: Pressure = force / area

= 500 / 1

= 500 N/cm2


Q8: What area is needed to produce a pressure of 300 Pa from a force of 125 N?

A8: area = force / pressure

= 125 / 300

= 0.42 cm2

 

Q6: Many stately homes insist that women wearing high heels remove them on entry. Explain why?

 

A6: The high heels concentrate the weight of the wearer over a small area, which causes high pressure and this can damage certain types of floor. Flat shoes allow the wearer’s weight to be spread out over a larger area, lowering the pressure.

 

 

 

 

 

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