Question

A clock hangs on the North wall of your bedroom. According to the "right-hand-rule", what is the direction of the rotational momentum of the minute-hand of your clock?

A. North
B. East
C. South
D. West

Answer 1

Using the right-hand rule, the angular momentum of the minute hand of the clock, which rotates clockwise when facing it, is directed into the North wall upon which the clock is hung. Your thumb, pointing into the wall, represents the direction of the angular momentum vector.

Step-by-step explanation:

To determine the direction of the rotational momentum, or angular momentum, of the minute hand of the clock, we use the right-hand rule. The right-hand rule is a mnemonic used in physics to determine the direction of parameters like angular momentum in a rotating system. When applying the right-hand rule, you align your right thumb with the direction of the rotation axis. As the minute hand of a clock rotates clockwise when facing it, you would curl the fingers of your right hand in the direction of the rotation (clockwise). Consequently, your thumb will point into the wall upon which the clock is hanging.

The direction that the thumb points to represents the direction of the angular momentum vector. Therefore, the angular momentum of the minute hand of the clock is directed into the North wall. This is analogous to the conceptual situation where Earth’s rotation is west to east, and by using the right-hand rule, the angular momentum vector points from the surface to the center of the Earth.