Pressure: the invisible push
What pressure really is, why it pushes in every direction, and why fluids always run from high to low.
⏱ 5 min
- Everyday comparisonStep 1 of 5
Squeeze the toothpaste
Squeeze a tube of toothpaste in the middle. The paste comes out of the opening — even though you pushed on the side, not the end.
Your push travelled through the paste in every direction. That push, spread over the inside of the tube, is called .
- WatchStep 2 of 5
Where does pressure come from?
Inside a closed box, the molecules of a fluid are constantly bumping into the walls. Every bump is a tiny push.
Millions of tiny pushes added together = pressure. The orange flashes show each bump on the walls.
- Try itStep 3 of 5
Squeeze the box
Now push the piston to make the box smaller. The molecules have less room, so they hit the walls more often.
Watch the pressure gauge climb. More bumps per second = more pressure.
Challenge: Make the box half as wide. What happens to the pressure — does it roughly double?
- ExplainedStep 4 of 5
Pressure pushes in all directions
Pressure is not just “downwards”. A balloon is round because the air inside pushes equally on every part of the rubber.
Deep water has more pressure, because of the weight of all the water above. Every 10 metres of water adds about 1 — that is why your ears hurt at the bottom of a deep pool.
- The impeller connectionStep 5 of 5
High to low, always
A fluid always moves from high pressure to low pressure, like a ball rolling downhill. Open a bike tyre valve and the air rushes out — from high inside to low outside.
That is the whole trick of a : its impeller creates higher pressure at the outlet, so water is pushed along the pipe to wherever you need it.
📌 Remember this
Pressure is the push of a fluid on every bit of surface around it. Fluids always flow from high pressure to low pressure — pumps create that difference.