Speed vs pressure
Why a narrow spot makes water faster, and why fast water has less pressure.
⏱ 6 min
- Everyday comparisonStep 1 of 5
Your thumb on the hose
Put your thumb over the end of a garden hose. The water suddenly shoots much further. Why?
The same amount of water must still get out every second, but the opening is now tiny. The only way through is to go faster.
- WatchStep 2 of 5
The crowd at the gate
Picture a crowd leaving a stadium. Where the corridor is wide, people stroll. At a narrow gate, they must hurry so that the same number of people get out each minute.
Water does exactly the same. Engineers call this rule : what goes in must come out.
- Try itStep 3 of 5
Squeeze the pipe
Drag the slider to make the middle of the pipe narrower. Watch the dots speed up in the narrow part.
Now look at the little glass tubes on top. They show the pressure: the higher the water in a tube, the higher the pressure below it.
Challenge: Make the pipe as narrow as possible. What happens to the water level in the middle tube?
- ExplainedStep 4 of 5
Two pockets of energy
Surprised? In the narrow part the water is faster, but its pressure is lower. This is .
Think of the water’s as money split between two pockets: a “speed pocket” and a “pressure pocket”. Moving coins from one to the other does not change the total. Speed up → pressure goes down. Slow down → pressure comes back up.
- The impeller connectionStep 5 of 5
The secret of every centrifugal pump
This is the most important idea in the whole course. An impeller throws water out very fast — all the energy is in the speed pocket.
Then the pump slowly widens, so the water slows down — and the energy moves into the pressure pocket. Fast water in, high pressure out. You will see this again in Module 2.
📌 Remember this
Where a pipe gets narrower, water goes faster and its pressure drops. Where it widens, water slows and pressure rises. Pumps use this to turn speed into pressure.