When you look at a clock and its hands are turning to the right you say this is clockwise. From the clock's perspective though, its hands are turning counterclockwise. Why?

All rotation is labeled from the POV of the person doing the turning. If you turn a bolt and screw around, rotate it 180 degrees, relative to you, the direction used to unscrew it seems to be reversed. It's just how things work.

That's only true if the clock is oriented differently from you, just like left and right mean different things to people with different orientations.

When people began making clocks, perhaps they continued to follow the same convention as sundials. Most of the earth's land (and the origins of western civilization) is in the northern hemisphere, where the shadow of sundial gnomons (pointers) begins the day in the west and then moves toward the north and then the east. The same convention holds true for the sun that casts those shadows: someone north of the equator, when facing south, sees the sun rise at their left, then it travels somewhat overhead, and sets to their right.

 

Edited December 20, 201015 yr by ewmon

That seems quite logical. Never thought of that, but it certainly makes sense.

Some applications use counterclockwise rotation as a matter of convention. I don't know why. I am thinking of voltage and current phasor diagrams. I quite like the sundial theory but interestingly some churches had sundials on their south facing walls where the movement of the shadow was anticlockwise. This link shows an example http://pandy.me.uk/sundials/carston.htm

Isn't simply that it would seem counter-intuitive to refer to the direction the hands are supposed to go as "counterclockwise." So, simply, we refer to the direction the hands are supposed to go as "clockwise" and therefore the opposite is "counterclockwise."