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# Pendulum law watch

1. Hi,

Can someone explain to me the laws of physics behind the pendulum? I have a brief understanding that it is to do with Hooke's law?

Specifically, I am interested in what happens when a pendulum does not obey Hooke's law.

If you could point me to some 'easy on the eyes' literature, or have a go at explaining it to me on this forum, I'd be very grateful.
2. (Original post by bluemohito)
Hi,

Can someone explain to me the laws of physics behind the pendulum? I have a brief understanding that it is to do with Hooke's law?

Specifically, I am interested in what happens when a pendulum does not obey Hooke's law.

If you could point me to some 'easy on the eyes' literature, or have a go at explaining it to me on this forum, I'd be very grateful.
Not sure if this classifies as easy on the eyes:
http://labman.phys.utk.edu/phys221/m...20pendulum.htm
3. (Original post by joostan)
Not sure if this classifies as easy on the eyes:
http://labman.phys.utk.edu/phys221/m...20pendulum.htm
That's kind of easy on the eyes, I no longer get spooked at funny looking letters

So, I'm actually interested in the physics for when a pendulum, or a spring (or anything that exhibits simple harmonic motion tbh) does not obey Hooke's law.
4. (Original post by bluemohito)
That's kind of easy on the eyes, I no longer get spooked at funny looking letters

So, I'm actually interested in the physics for when a pendulum, or a spring (or anything that exhibits simple harmonic motion tbh) does not obey Hooke's law.
Hooke's law only applies to springs, so technically, anything that is not a spring does not obey Hooke's law. . .
5. (Original post by joostan)
Hooke's law only applies to springs, so technically, anything that is not a spring does not obey Hooke's law. . .
Ahh, yes.

In simple harmonic motion, the motion is that of a sine curve. This I understand. What would be the motion of an object that did not obey simple harmonic motion, say for example, a pendulum whose amplitude is beyond the control of simple harmonic motion.
6. (Original post by bluemohito)
Ahh, yes.

In simple harmonic motion, the motion is that of a sine curve. This I understand. What would be the motion of an object that did not obey simple harmonic motion, say for example, a pendulum whose amplitude is beyond the control of simple harmonic motion.
Then the motion is not sinusoidal.
The maths then becomes very tricky because the restoring force is not proportional the the displacement. (The condition required for SHM.)

If you really want to take a look at the maths it is found on this page.
Starts with small angle then looks at large angle.

http://en.wikipedia.org/wiki/Pendulum_(mathematics)

An interesting way of finding out what the non-SHM motion looks like is to solve the equations numerically, rather than analytically as in the link above.
7. Try double or multiple pendula, you end up getting something completely different.

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