Thread: Hands of a Clock Constant Velocity?

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

This question confused me a little bit at first, because the hands of an ordinary clock do not move at a constant rotational speed. They move in a jerky stepwise motion, which you can see by watching the second hand. But assuming they were moving smoothly, d would be the only right answer. There is a difference between speed and velocity. Velocity is a vector. An object moving at a constant speed in a circular motion is accelerating, because the velocity is constantly changing.

Always digital

Even with a seemingly smooth sweeping second hand, the motor driving this has a digital action.

Anyone who has programmed a stepper motor in low level machine code i.e a computer techy will confirm this.

Originally Posted by tszy

Always digital

Even with a seemingly smooth sweeping second hand, the motor driving this has a digital action.

Anyone who has programmed a stepper motor in low level machine code i.e a computer techy will confirm this.

i agree with this guy...

time is always on queue/cue with digital clocks

what is time? dude they should make a watch, and call it the atomic graviton.

Ya only d) is correct, the speed (ideally) would be constant, since speed does not include direction. The velocity is constantly changing (as Harold pointed out) since the direction is changing (and velocity as a vector includes direction) so the velocity is constantly changing.