# I Physics Behind a Fan

1. Jun 26, 2017

### STAR GIRL

Fan makes me wonder the Vicinity of Physics. The fan is rotating at an anti-clockwise direction & it is suspended from the ceiling by a cylindrical handle. Now the fun starts here...

According to Newton's 3rd law every action has its opposite reaction. That means the anti-clockwise angular momentum of the fan should produce a clockwise torque on its handle which will make the handle unstable & forces the fan to fall down.

But this never happens why?

2. Jun 27, 2017

### rcgldr

At steady state (not accelerating), the motor exerts an anti-clockwise torque on the fan, the fan exerts an anti-clockwise torque on the air related to drag. The air exerts a clockwise torque on the fan, which in turn exerts a clockwise torque on the motor, which in turn exerts a clockwise torque on the handle, which in turn exerts a clockwise torque on the ceiling (the "ceiling" would exert an anti-clockwise torque on the handle).

3. Jun 27, 2017

### Staff: Mentor

Constant angular momentum does not produce torque; the drag of the fan against the air is what produces the torque.
It isn't much torque.

4. Jun 28, 2017

Thanks