Which part of an angular velocity vector is its direction?

Question

I am assuming that an angular velocity vector only has two direction: positive for counterclockwise and negative for clockwise.

Just to make sure that I have the right interpretation.

Newton's 1st law states:

An object remains in a state of uniform rotational motion unless acted upon by a net torque. ("In a straight line" is taken out)

This means that the speed of the angular velocity vector is constant. However, even without an net torque, the direction will change. how?

Edit. I just googled Newton's 1st Law. It only says uniform motion in a straight line. Does it mean the object can travel back and forth along the line?

Understand the vector of angular momentum better, here: http://physics.stackexchange.com/q/219890/ . Newton's 1st applies to pure rotation as it does to pure translation. — Gert, Nov 22 '15 at 16:14
@Gert, how to we measure the angle between the force and position vectors? Sin270 will be -1. — most venerable sir, Nov 22 '15 at 17:41
I'm not sure what you mean. So $\sin 270^\circ=-1$, so what? — Gert, Nov 22 '15 at 17:52
@Gert, my book did not limit the range of theta to [0, 180]. (Formula: t=rFsintheta) — most venerable sir, Nov 22 '15 at 17:53
It doesn't have to: an angle is an angle is an angle, period. — Gert, Nov 22 '15 at 18:02
But the direction is different. The sign of toque is different. — most venerable sir, Nov 22 '15 at 18:03

score 1 · Answer 1 · answered Nov 22 '15 at 16:45

1

By uniform motion in a straight line, the law refers to both its magnitude and direction. You can't go back and forth without a force.

answered Nov 22 '15 at 16:45

Raj Batra

11

Which part of an angular velocity vector is its direction?

1 Answers1