What is Pressure?

Lil Engineers!

An educational resource to help understand the basic concepts of pressure

Pressure can be explained as the amount of force on a certain area.

Believe it or not, the air surrounding you has pressure, it is called atmospheric pressure. It usually reads a bit over 1 bar, but if you look at your weather app it might tell you something around 1015hPA (this is just a different unit of measurement, there are 1015 hPA in 1.015 bar… For this exercise we will keep things simple and refer to everything in the bar unit).

Interestingly, the atmospheric pressure is different depending on where you live, and is also affected by the weather.

Pressure can be found everywhere!

The weight of your body standing on the ground has pressure, the liquid you pour through a funnel has pressure.

Although it may seem like an invisible force, sometimes we can see it in action. If we look around the house, maybe we can find some examples of things that are “pressurised” around your house, these are things where the pressure is higher than the outside pressure.

Can you think of anything around the house that is pressurised?

Here’s one to get you started

Turn on a tap! See how the water gushes out… this is because it is pressurised in the hoses that lead to it. Often the water we get in our taps is stored in a reservoir in the highest point nearby, maybe a hill or a water tower. Then it travels through pipes to your house which is lower than the water reservoir, which creates pressure allowing it to push out of your taps. In Australia, the ideal standard for water pressure is 5 bar. This is an example of water pressure.

Are there any other things that you can think of that have water pressure?

What about water guns! Without going into detail about the mechanics of a water gun, we can at least understand that in order for water to squirt out and hit your friend or sibling, it has to be pressurised!

These are easy to see because water is visible, but what about air? We know that the air around us has pressure (around 1 bar) so…

Can you think of any examples where you might find air that has more pressure?

The tyres in a bike or car do! Have you ever had to “pump up your tyres”? An air pump compresses air and pushes it into your tyres to inflate them, this makes your tyres bouncy and reduces the feeling of bumps and lumps while you’re moving.

Bike tyre pressures vary depending on the type of tyres, the ideal pressure can range anywhere from 1.7 bar to 8 bar!

Car tyre pressure doesn’t vary as much, and they usually are around 2.2-2.6 bar.

Are there any other things that you can think of that have air pressure?

We just spoke about inflating tyres… what else can be inflated?

Balloons! When we blow air into a balloon, we are creating air pressure that inflates the balloon. And the same goes for blowing up inflatable pool toys!

What do we use pressure for?

Now we can see that pressure is all around us in our homes, we can think about how it is used in an industrial setting.

Pressure is INCREDIBLY useful in manufacturing for example. We can use it to make objects move, we can use it to detect faults, we can use it to clean, it is utilised in almost every aspect.

What is an example of pressure being used in industry?

Here is one way we can use pressure in industry. Let’s have a look at the image below.

The device on the left is called a cylinder, inside is a piston rod that can move left to right. Here it is not pressurised, and the rod is in it’s resting position to the left.

What would happen if we added pressure to the left hand side of the rod by pushing air in?

We can see that pushing pressurised air into the left side of the cylinder, the piston rod moves to the right and extends it’s foot, which pushes the box!

This is a simple demonstration of how pressure can be utilised.

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