# X= Acos(wt)? X= Asin(wt)?

1. Oct 18, 2009

### SAT2400

X= Acos(wt)?? X= Asin(wt)??

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

X= Acos(wt)??

X= Asin(wt)??

Which is right? in some books, x = A sin(wt), while in other books, x= Acos(wt)...

I'm confused.

Please explain this to me. Thank you very much.

2. Oct 18, 2009

### rl.bhat

Re: X= Acos(wt)?? X= Asin(wt)??

. f(x) is the projection of a particle moving in a uniform circular motion with radius A and angular velocity ω. If you take the projection on x-axis, then f(x) = Acosωt.
Ιf you take the projection on y axis, then it is f(x) = Asinωt

3. Oct 11, 2011

### ventura23

Re: X= Acos(wt)?? X= Asin(wt)??

use x=Asin(wt) if the oscillation is starting from the equilibrium position (b/c if u look at a sin curve, it starts at a value of 0), and if it is starting at the amplitude, use x=Acos(wt). (b/c looking at a cosine curve, it starts at the amplitude)

But since sin and cos are really the same functions except shifted over, these two equations are both true and essentially mean the same thing.