Posted by charlie on .
Am self studying SHM, so sorry for the elementary questions.
Would someone check/confirm some facts i think I've learned please.
1 If a sine wave graph starts at the origin at time = 0s, the sysyem is in equilibrium?
2 The amplitude at t= 0s is zero.
3 Same system, the phase angle/constant (phi) is 0 or pi?
4 When a system is displaced, but at rest, the phase angle is + or  half pi?
Confirmation or advice appreciated
Thanks

Physics SHM 
bobpursley,
1. What does the sine wave represent?
2. Yes. If your sine wave is amplitude.
3. This makes no sense.
4. yes. 
Physics SHM 
charlie,
Sorry Bob,
The wave represents a simple pendulum.
In 3, I'm referring to the equation
x(t)=Asin(wt+(greek letter phi)), so was looking to confirm that in that specific circumstance I outlined, the value of phi would either be zero or pi (as in 22/7).
Thanks.