4.5 Pressure on solids
Summary: When astronaut Neil Armstrong walked on the Moon in 1969, he left footprints. The footprints are still there, which you can see in Figure 1. Tags: science oxford-science student-book-7 physics Created: 2026-05-19 Last Updated: 2026-05-19
Key words After this topic, you will be able to:
- describe Pressure on a solid, and give the direction that it acts in
- calculate pressure
- describe situations where high or low pressures are useful.
Think back
- State the direction of gas and liquid pressure on a surface.
- State the unit of force.
- State two units of area. Key idea Pressure on solids is a measure of how much force is applied over a given area. We can measure pressure in newtons per metre squared (N/m2). Key words pressure, newtons per metre squared (N/m2), pascal (Pa)
When astronaut Neil Armstrong walked on the Moon in 1969, he left footprints. The footprints are still there, which you can see in Figure 1**.**
Figure 1Figure 1 There is no wind on the Moon to blow Neil Armstrong’s footprints away.
What is pressure on a surface?
When you stand on any surface, you exert (apply) a force on it because of your Weight. Your weight is spread out over the area of your foot. You are exerting a pressure on the ground. If you are standing on a soft surface, such as mud, the pressure might be big enough for you to sink (slowly go down below the surface of the mud).
Look at the machine in Figure 2. An earthmover is very heavy. It has a weight of about a million newtons. This is the same as about 15000 people! A single person standing on the same muddy ground might sink. The earthmover does not sink because its weight is spread out over a bigger area.
Figure 2The tracks on the earthmover stop it sinking into the mud.
Pressure is a measure of how much force is applied over a certain area. The pressure acts in a direction that is at 90°, or normal, to the surface.
A Compare the direction of gas and liquid pressure with pressure on a surface.
How do you calculate pressure?
You calculate pressure using this equation:
You measure force in newtons (N) and area in metres squared (m2).
Pressure is measured in newtons per metre squared (N/m2). 1 newton per metre squared is also called a pascal (Pa).
Sometimes it is easier to measure smaller areas in centimetres squared (cm2). If you measure the area in cm2, the pressure is measured in N/cm2.
When you do calculations, it is very important to look at the units of area.
B State three units of pressure.
What produces big and small pressure?
Hockey and football boots have studs. These are pieces of plastic or metal that stick out from the bottom of the boot. They have a small area compared with the area of the foot (see Figure 3). This produces a bigger pressure. The studs sink into the ground and help the player move quickly.
Figure 3Studs on hockey or football boots have a small area. This produces a big pressure, so you sink into the ground. This increases grip on the ground while playing sports.
The weight of a hockey player is 600N.
The area of their two feet is 200 cm2.
The total area of the studs is 20cm2.
Studs on shoes increase the pressure, as do sharp knives and nails.
The tracks on earthmovers (see Figure 2), snowshoes (see Figure 4), and wide straps on backpacks decrease the pressure. To produce the same pressure on the floor that you exert when you push in a drawing pin, you would need over5000 people standing on yourshoulders.
Figure 4Snowshoes have a big area. This produces a small pressure, so you do not sink into the snow.
C Explain why wide straps on backpacks decrease the pressure.
Maths skills Change the subject to work out the correct equation for calculating force.
- A force = pressure ÷ area
- B force = pressure = area
- C force = area ÷ pressure
Stretch zone
- Copy and complete the sentences. Pressure is a measure of how much force/pressure there is on a certain area/volume. If you exert a big/small force on a big/small area the pressure will be large. Pressure can be measured in N/m2 / Nm.
- A gymnast has a weight of 600 N. The area of each hand is 150 cm2. Calculate the pressure on the floor when they are doing a handstand.
Stretch zone
- Atmospheric pressure is 101 kPa, or 101 kN/m2. Assume the top of a car has an area of 1.5 m2. Calculate the force of the atmosphere on the top of a car.A giant panda has a weight of 1000 N. Calculate the number of giant pandas that would have to sit on the top of your car to exert the same force as the atmosphere.Explain why your car does not collapse under the weight of the atmosphere.