- #1
jaumzaum
- 434
- 33
I was trying to understand why a spring -mass assembly and a simple pendulum is a simple harmonic movement.
I've done like this:
In a SHM that starts in -A, we have x = -A.cos(wt)
In a spring-mass we have that the maximum velocity is [itex] \frac{mv²} {2} = \frac{kA²}{2} -> v = A\sqrt{\frac{k}{ m}} [/itex]
[itex] w = v/A = \sqrt{\frac{k}{m}} [/itex]
[itex] v = \int a.dt = \int \frac{-k.x}{m} dt [/itex]
But in a SHM, [itex] v = -w .x.tan(wt) -> -w .x.tan(wt) = \int \frac{-k.x}{m} dt [/itex]
If we substitute x = -A.cos(wt), we see that the expression is true, so spring-maass is a SHM.
But I don't know how to demonstrate why pendulum is a SHM?
I've done like this:
In a SHM that starts in -A, we have x = -A.cos(wt)
In a spring-mass we have that the maximum velocity is [itex] \frac{mv²} {2} = \frac{kA²}{2} -> v = A\sqrt{\frac{k}{ m}} [/itex]
[itex] w = v/A = \sqrt{\frac{k}{m}} [/itex]
[itex] v = \int a.dt = \int \frac{-k.x}{m} dt [/itex]
But in a SHM, [itex] v = -w .x.tan(wt) -> -w .x.tan(wt) = \int \frac{-k.x}{m} dt [/itex]
If we substitute x = -A.cos(wt), we see that the expression is true, so spring-maass is a SHM.
But I don't know how to demonstrate why pendulum is a SHM?