Hands of a Clock Constant Velocity?

[WriterTyper]

Hi Folks,

What I have here is a multiple choice question from a practice test. I believe there to be two right answers but the answer key says there's only 1. I'm not looking for anyone to do my homework for me, I just think there is a mistake. Here we go:

The hands of a clock _______.

a) have a constant velocity c) constantly change speed
b) have no momentum d) are accelerating

Now I know for sure that d is correct because there is a diagram of this very question in the book! Any object when has a change in it's motion is accelerating, regardless of speed.

BUT...aren't the hands of a clock going in a constant speed and direction? So wouldn't they have a constantly velocity? Meaning that "a" is right as well? I thought that moving in a circular path was considered to be constant direction and hence, with constant speed, to mean constant velocity.

If I'm wrong please explain why...this has been bothering me for a few hours.

Thanks!
WT

 

[Doc Al]

Now I know for sure that d is correct because there is a diagram of this very question in the book! Any object when has a change in it's motion is accelerating, regardless of speed.

Acceleration is a measure of the rate of change of velocity. Whenever the velocity changes, there's an acceleration.

BUT...aren't the hands of a clock going in a constant speed and direction?

Are they? What direction does the hand move when pointing at 12 versus when pointing at 6?

So wouldn't they have a constantly velocity? Meaning that "a" is right as well? I thought that moving in a circular path was considered to be constant direction and hence, with constant speed, to mean constant velocity.

While the speed doesn't change for uniform circular motion, the direction is constantly changing. Imagine someone running around a circular track at constant speed. Are they always going in the same direction?

 

[WriterTyper]

Ah ha, thanks Doc Al. So the hands are constantly changing direction, and hence constantly changing velocity. And since the velocity is constantly changing, the hands are accelerating. D is the only answer: there is no mistake.

So can we say that a perfect circular movement is, in a way, the complete opposite of constant velocity?

Thanks again,
WT

 

[Doc Al]

So can we say that a perfect circular movement is, in a way, the complete opposite of constant velocity?

I'm not sure what 'complete opposite' would mean, but it's definitely not constant velocity. Velocity can change in two ways: the speed can change or the direction can change (or both). Uniform circular motion is an example of just direction changing.