Angled blades catching moving air
How Does a Windmill Turn?
Angled blades deflect moving air sideways, and the air pushes back, spinning the rotor.
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Step 1 of 5
Wind is air with momentum.
Moving air carries real energy. Slowing it down means that energy has to go somewhere — into the blades.
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Step 2 of 5
The blades are angled, not flat.
A blade square to the wind is just pushed backwards. Angled, it deflects air sideways and generates a turning force instead.
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Step 3 of 5
Deflecting air pushes the blade around.
Push air one way and it pushes you the other. That reaction force acts at a distance from the hub, so it turns the rotor.
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Step 4 of 5
Blade twist keeps it working along its length.
The tip travels much faster than the root, so it meets the wind at a different angle. Blades are twisted to stay efficient all the way out.
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Step 5 of 5
It can never take all the energy.
Air must keep moving to get out of the way. Physics caps a wind turbine at about 59 percent of the wind's energy.
Windmills ground grain and pumped water for centuries before anyone used them to generate electricity.
The short version
Windmills turn because angled blades deflect moving air sideways and the air pushes back, spinning the rotor.
Try it yourself
Hold a paper pinwheel square to a fan, then tilt the blades. Only the tilted blades spin.
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