Pressure - CCEA

• Pressure is a force exerted per m², the unit of pressure is the pascal (Pa), where 1 Pa = 1 N/m².

• The equation P = F ÷ A is used to calculate pressure.

• When using a sharp knife, the small area of the blade creates a large pressure, making cutting easier.

• Having caterpillar tracks on vehicles means their weight acts over a large area, so reducing the pressure they exert on the ground.

Pressure is the effect of a force over an area.

It is the force acting over 1 m².

Therefore, the definition of pressure is: pressure is the force per unit area.

If a force acts over a larger area, then the pressure will be smaller.

If the same force acts over a smaller area, then the pressure will be larger.

Exam Tip

You should never refer to the area as the “surface area” as this would include the whole outer surface of the object not just the area in contact.

You should just use simply area or contact area.

When answering descriptive questions about pressure, you must talk about the force that is acting and the area over which it acts.

You then state whether this combination leads to a larger or smaller pressure.

The unit of pressure is N/m² or pascal, Pa.

1 N/m² = 1 Pa

For smaller areas, the units N/cm² and N/mm² are also used for pressure.

Pressure is only in pascals, Pa, when the force is in N and the area is in m².

A pressure of 50 Pa means that a force of 50 N acts over an area of 1 m².

When the units of force are newtons (N) and the units of area are square metres (m²), then the units of pressure are N/m², which are commonly called pascals (Pa).

In calculations, the units for pressure may be in N/cm² or even N/mm².

Use the units that the question provides – you will not be expected to convert mm² or cm² to m².

Pressure is important in a range of everyday situations.

• Different styles of shoe can cause different pressures due to their area.

• Flat shoes spread the force over a large area, reducing the pressure. Snow shoes have a much larger area than feet to spread the force over a larger area and reduce the pressure on the snow, this stops people sinking into the snow.

• High heeled shoes or boots transfer the force through a much smaller area, causing a much greater pressure. It will hurt more if a person steps on someone’s foot in high heels than if they are wearing flat shoes.

• When using a sharp knife, the small area of the blade creates a large pressure, making cutting easier.

• Having caterpillar tracks on vehicles means their weight acts over a large area. This reduces the pressure they exert and are less likely to sink in to wet ground.