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# AQA Physics Sine waves and SHM watch

1. Just a bit stuck atm, I was reading about sine wave solutions and i understand the proof of how a bob on a pendulm swing has motion that resembles circular motion. I also get how a(x)=-w^2x and that x=Acos(wt), where x is the displacement. However, I don't get how the general formula is derived. E.g. x=Asin(wt + phase difference). Like I thought the cos was meant to relate to the fact that we're considering displacement in the x axis only. But using sine would mean we're considering the y axis, so how does the formula suddenly change. Could someone kindly explain this?
2. I've got a test tomorrow could anyone help please?
3. (Original post by funky2722)
Just a bit stuck atm, I was reading about sine wave solutions and i understand the proof of how a bob on a pendulm swing has motion that resembles circular motion. I also get how a(x)=-w^2x and that x=Acos(wt), where x is the displacement. However, I don't get how the general formula is derived. E.g. x=Asin(wt + phase difference). Like I thought the cos was meant to relate to the fact that we're considering displacement in the x axis only. But using sine would mean we're considering the y axis, so how does the formula suddenly change. Could someone kindly explain this?
I am sorry for the late reply. Both cos and sin function are inter-related.

The "so-called" general formula can be a sin or cos function which does not change the physics of oscillation.

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