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.

 

[rwisz]

Hello WT,

You are correct in your thinking that the hands of a clock have a constant velocity. Velocity is a vector quantity, meaning it has both magnitude (speed) and direction. In the case of a clock, the hands are moving at a constant speed in a circular path, but their direction is constantly changing. This means that their velocity is also constantly changing, even though their speed remains the same.

The answer key may be referring to the fact that the hands of a clock do not have a constant linear velocity, as they are moving in a circular path. However, in physics, velocity refers to the instantaneous rate of change of an object's position, so the hands of a clock do have a constant velocity at any given moment in time.

I hope this explanation helps clear up any confusion. Keep up the good thinking!