Homework Help: Equal to zero if angular velocity is constant

darkmagic · Mar 13, 2010

1. The problem statement, all variables and given/known data

Which is equal to zero if angular velocity is constant, normal or tangential acceleration?
The one with zero angular velocity is a crank. The crank moves at a fixed point.

2. Relevant equations

3. The attempt at a solution

rock.freak667 · Mar 13, 2010

Re: acceleration

darkmagic said: ↑

3. The attempt at a solution

So which do you think it is and why?

darkmagic · Mar 14, 2010

Re: acceleration

I think it is the tangential one because that means it is a uniform motion but continuously changing speed? is that correct?

rock.freak667 · Mar 14, 2010

Re: acceleration

darkmagic said: ↑

I think it is the tangential one because that means it is a uniform motion but continuously changing speed? is that correct?

But it is not changing speed, the angular velocity is the same.

At different points in the circular motion, if you draw a tangent to the circle, you will get the direction of velocity right? Does this tangent always point in the same direction?

darkmagic · Mar 14, 2010

Re: acceleration

sorry it should be constant velocity. changing direction but constant speed, right?

rock.freak667 · Mar 14, 2010

Re: acceleration

darkmagic said: ↑

sorry it should be constant velocity. changing direction but constant speed, right?

Yes. So would the tangential velocity be changing is α is defined as α=dω/dt ? Since the direction of the tangential velocity is changing what does that say about acceleration?

darkmagic · Mar 14, 2010

Re: acceleration

velocity is changing. If that is changing, acceleration is also changing?

rock.freak667 · Mar 14, 2010

Re: acceleration

darkmagic said: ↑

velocity is changing. If that is changing, acceleration is also changing?

Right so if you were to draw the two velocity tangents and then find the change in velocity, it would point towards the center of rotation. So which acceleration is zero?

darkmagic · Mar 14, 2010

Re: acceleration

Normal acceleration is always towards the fixed point. The normal one?

rock.freak667 · Mar 14, 2010

Re: acceleration

darkmagic said: ↑

Normal acceleration is always towards the fixed point. The normal one?

That would be correct.

darkmagic · Mar 14, 2010

Re: acceleration

Can you give a summary on how to determine which is zero among the two in different situations?

How can I determine the tangential acceleration if I have given the angular velocity?

rock.freak667 · Mar 14, 2010

Re: acceleration

darkmagic said: ↑

Can you give a summary on how to determine which is zero among the two in different situations?

How can I determine the tangential acceleration if I have given the angular velocity?

tangential acceleration is related to α by a_tangential=αr

darkmagic · Mar 14, 2010

Re: acceleration

so, if normal is zero, then tangential equals the angular acceleration. I only depend on the tangential and normal formula.

rock.freak667 · Mar 14, 2010

Re: acceleration

darkmagic said: ↑

so, if normal is zero, then tangential equals the angular acceleration. I only depend on the tangential and normal formula.

no no, the only way for your normal acceleration to be zero is if the object is not spinning. Remember a=ω²r

darkmagic · Mar 14, 2010

Re: acceleration

so normal is zero in a sliding block?

rock.freak667 · Mar 14, 2010

Re: acceleration

darkmagic said: ↑

so normal is zero in a sliding block?

You mean a sliding block on a curved surface? No, the normal is not zero. In that case there is still a normal acceleration.

darkmagic · Mar 14, 2010

Re: acceleration

i mean in a mechanism, in a flat surface. the sliding block has zero normal? I'll be back.

rock.freak667 · Mar 14, 2010

Re: acceleration

darkmagic said: ↑

i mean in a mechanism, in a flat surface. the sliding block has zero normal? I'll be back.

Once your object is basically rotating with respect to some point, there will be a normal acceleration.

darkmagic · Mar 14, 2010

Re: acceleration

I mean in a mechanism, the sliding block, the normal in a flat surface is zero?

rock.freak667 · Mar 14, 2010

Re: acceleration

darkmagic said: ↑

I mean in a mechanism, the sliding block, the normal in a flat surface is zero?

ok, what sort of mechanism are you talking about?