Real life applications to the simple pendulum experiment I have been wondering quite lately what were the real life applications used in a simple pendulum experiment. Time measurement is one of the applications that could be used for simple pendulum experiment but is nevertheless, affected by length. What other applications are there for simple pendulum that may also be affected by length?
 A: An useful real application of the simple pendulum may be the calculation of the Earth's gravity $g$. Knowing the period $T$ and the length $l$ you can estimate the gravity with this simple equation: $$T=2\pi\sqrt{\frac{l}{g}}$$ and so reversing it: $$g=\frac{4\pi^2l}{T^2}$$
Remember that this equation is only true if you consider small fluctuations of your pendulum.
The fundamental topic behind is simple harmonic motion.
This type of motion covers topics from classical mechanics to quantum mechanics and so on...
It's also important to know that if you had a rigid body instead of a material point, the length would also depend on the shape of the body. It would become an "effective length".
Another example that could serve as an answer to you is the verification of the existence of apparent forces when you hold a simple pendulum and you are in a non-inertial reference system, like a bus after the bus stop. You see that, when you are accelerating the material point has a new equilibrium point due to apparent forces.
