An actual question my five year old asked me and I couldn’t answer, please help!
In: Physics
Next time you’re in a swimming pool try moving your hand through the water as fast as you can. Change the angle a bit and notice that you push more or less water around. Now try it again with your whole arm under water. You can push more water around but it also requires much more effort.
Propellor optimization (fans are just propellers) involves striking a balance between the amount of fluid you want to move at the energy used to move it. Increasing the surface area of the propellor will move more fluid but require more energy to operate. This can be achieved by increasing either the size of the blades, the number of blades, or both.
A house fan only needs to move relatively little air at high efficiency. A speedboat propeller is going to be optimized to move water. Many airplanes also have the ability to change the angle of their blades, taking a larger or smaller “bite” out of the air without changing the surface area exposed to the medium.
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