Impeller vs propeller vs turbine
Three spinning machines that look alike but do opposite jobs.
⏱ 5 min
- Everyday comparisonStep 1 of 6
Fan or windmill?
A desk fan and a windmill look alike: blades on a shaft. But a fan uses electricity to push air, while a windmill uses moving air to make electricity.
Same shape, opposite direction of energy. Keep that in mind — it is the key to this whole lesson.
- Try itStep 2 of 6
Three machines, side by side
Switch between the three machines. In each one, water flows from left to right.
Watch the colour: orange water has gained energy, blue water has less. Where does the energy go in each case?
Challenge: In which machine does the water leave with less energy than it came in with?
- ExplainedStep 3 of 6
Impeller: closed in, building pressure
An works inside a casing and its goal is usually pressure (and flow) in a pipe. A motor gives it energy; it passes that energy to the fluid.
- ExplainedStep 4 of 6
Propeller: open water, making thrust
A works in open water or air. It throws fluid backward, and — just like a skateboarder throwing a heavy ball — gets pushed forward. That push is .
It does not try to build pressure in a pipe. It just wants to move itself (and the boat) along.
- ExplainedStep 5 of 6
Turbine: taking energy out
A does the opposite of an impeller. Fast or high-pressure water pushes on its blades and spins it; the shaft then drives a generator.
Fun fact: some ordinary pumps are run backwards as small turbines, making electricity from water flowing downhill. Same machine, opposite job.
- The impeller connectionStep 6 of 6
The general word: rotor
Engineers call any spinning part a . Impeller, propeller, turbine wheel and fan are all rotors — named after the job they do.
In the next module you will see that impellers themselves come in many shapes, some of which look a lot like propellers.
📌 Remember this
An impeller gives energy to a fluid inside a casing (to make pressure and flow). A propeller throws fluid backward in open water to make thrust. A turbine takes energy out of a moving fluid.