# SHM question

1. Dec 9, 2006

### joker_900

1. The problem statement, all variables and given/known data
OK I haven't been given a definite question with values, but how would you find the natural frequency of a system of two pendulums coupled by a spring?

2. Relevant equations
a= -gx/l
T=2pi sqrt(l/g)

3. The attempt at a solution
Well the thing is, I know I need to consider each pendulum/spring separately and get two equations of motion, but I'm not sure how. All i know about pendulums are those two equations above. When I've had similar problems with springs I've been able to find the resultant force as a function of x and go from there. But in this case I just came up with the resultant -mgx/l - lamda(x-0.5l) = ma

Help!

2. Dec 9, 2006

### physics girl phd

Some thoughts:
Have you drawn out a picture of the system? Are the pedulums fixed at the same point at the top or are their top points separated by the natural length of the spring?

Then: Can you use free body diagrams to find out the forces on the bobs of the pendulums? What if you displace one bob in the system by a small angle?