# Homework Help: Solid State Physics: Atomic chain oscillations

1. May 29, 2015

### skrat

1. The problem statement, all variables and given/known data
Ok, don't get angry with me. The original problem is from Solid State Physics but my problem is very well in "Introductory physics". Here is the problem:

The chain consists of molecules, which has three atoms, each with mass $M$. Spring constant between the atoms inside the molecule is $K$ and between the molecules $Q \ll K$ as shown in the picture.

Now
part a) wants me to do "something" and use approximation that the molecules are rigid.
part b) wants me to do "something else" and use approximation that the molecules are not connected with a spring.

2. Relevant equations

3. The attempt at a solution
Now both of these approximations in part a) and b) should tell me something about the spring constants $Q$ and $K$. But I can't figure it out.

I am assuming that part b) wants me to set $Q\rightarrow 0$ while I have absolutely no idea what part a) is supposed to say. Maybe that $K\rightarrow \infty$?

2. May 29, 2015

### tech99

It looks as if the system has two resonant frequencies, and the two are independent.

3. May 29, 2015

### haruspex

Sounds right.