why do fans only blow air out of one side?
In: Physics
They only go in one direction and the blades “throw” the air one direction and “dig” air from the other direction with blades. Some ceiling fans have the option to go in both directions but small spatial fans likely don’t for ease of use.
Think of a fan blade as a shovel. A shovel slices into the dirt and moves earth out of the hole you’re digging. To make the hole deeper, you have to keep moving the shovel further into the bottom of the hole/the ground because the ground is solid and doesnt fill behind itself.
A fan blade is like a shovel attached to a spinning hub. It “digs” into the air, slicing it, and pushing it in the direction that the fan blade is tilted.
For example. A vertical fan pointing to the right, with blades like this, from the side:
/
Will spin (in this “diagram” anyway) from the top down, and push air that way. The bottom of the / is what “cuts” into the air. Since it cuts at an angle, the air is pushed by the wedge and that’s what transfers the kinetic energy from the fan blade to the air.
Since air DOES fill in behind itself, the only part of the fan that really has to move are the blades, on that spinning hub. This is also why if you put a piece of paper behind a desk fan, it will stick to the fan; the air that rushes in to fill the “hole” being dug by the fan blades creates a small current, that flows around the paper and can hold it there.
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Why do you only feel the wind moving on one side though? The air flowing in must equal the air flowing out, so why does it only feel cool and breezy on one side and not the other?
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