# What does the phase angle phi mean in the harmonic oscillation function?

1. Oct 10, 2012

### CrazyNeutrino

The function for simple harmonic oscillation is:
Acos(ωT)+$\phi$
Why is there an angle phi added to the function acos(ωT)?

2. Oct 10, 2012

### rudolfstr

it's Acos(ωT+ϕ) omega stands for how fast it' s oscilating, but phi determines the initial position( wold be Acosϕ)

3. Oct 10, 2012

### Shan K

I was reading a book on wave and found that when they derive the equation of shm from the equation force varies with negetive displacement , they had taken a propotionality constant to make the force and displacement equal and they had taken frequency of the shm as the constant . So my question is , is there any derivation which can show that the constant is the frequency of the shm .

4. Oct 10, 2012

### CrazyNeutrino

If phi had a value, what would the shm graph look like? Or how would it change from Acos(wT)?

5. Oct 11, 2012

### rudolfstr

The graph would change from sine to cosine, (remember, that sin(x+π)=cosx)

6. Oct 11, 2012

### CrazyNeutrino

7. Oct 11, 2012

### CrazyNeutrino

so how could it change from sine if it doesnt start at sine?

8. Oct 11, 2012

### rudolfstr

It never started as cosine, it's allways either sine or cosine or somethin in between. It's like you move the cosine a bit to the right and if you move it by π/2 you get sine! SO all phi determines is the initial position!

9. Oct 12, 2012

### CrazyNeutrino

Ok... Thanks! I almost understand.