# Normal modes, 2 masses, 2 springs

1. Jul 20, 2007

### Hume Howe

1. The problem statement, all variables and given/known data
hey, this is my first time using this forum and was wondering if i could have some help with this normal modes question.

suspended from a ceiling is in order: a spring of spring constant ($$k_{2}$$), a mass (m), a spring with spring constant ($$k_{1}$$), and another mass (m)

calulate the normal mode frequencies $$\alpha_{1}$$, $$\alpha_{1}$$ sorry can't find the omega symbol.

attempted solution:
let the displacement of the higher mass be x and the displacement of the lower mass be y.

m$$\ddot{x}$$=-$$k_{2}$$x + $$k_{1}$$(y-x)
m$$\ddot{y}$$=-$$k_{1}$$(y-x)

$$\left| \alpha^{2} - (\frac{k_{2}}{m} + \frac{k_{1}}{m}) -----\frac{k_{1}}{m} \right|$$
$$\left| \frac{k_{1}}{m} -------- \alpha^{2} - \frac{k_{1}}{m} \right|$$ = 0

determinant = 0

so $$\alpha^{2}$$ = 1/2[ ($$\frac{k_{2}}{m}$$+ $$\frac{2k_{1}}{m}$$) +- sqrt[($$\frac{k_{2}}{m}$$+ $$\frac{2k_{1}}{m}$$)^2 – 4($$\frac{k_{2}*k_{1}}{m^2}$$)]]

after simplifying it doesn't work when I use to try and solve for the amplitude ratios.
p.s. is there a simpler equation writer i could download and use here or should i just persevere and try to use this embedded one?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution