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The most accurate way to model a pendulum (without air resistance) is as a differential equation in terms of the angle it makes with the vertical, θ, the length of the pendulum, l, and the acceleration due to gravity, g.

d²θ/dt² = -g*sin(θ)/l

There is no easy way to integrate this to get θ as a function of time, but if you assume θ is small, you can use the small angle approximation sin(θ)~θ which makes the equation

d²θ/dt² = -g*θ/l

Which can then be integrated to get the solution

θ(t)=θmax*sin(t*√(g/l))

Using this equation, you can easily derive that the period of the pendulum (time required to go through one full cycle) would be

T=2π*√(l/g)

If air resistance is also accounted for in the original differential equation, the exact equation will be much harder to derive, but in general will involve an exponential decay of a sin function.

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15y ago

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Q: What is the equation for pendulums?
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