Let us assume that each of the springs admits Hooke’s law with a corresponding coe
ffi
cient
k
i
and the bodies
have masses
m
1
and
m
2
, respectively. We assume that at
t
= 0 the system is perturbed away from its equilibrium
state, and we wish to solve for the position of the bodies
y
1
(
t
) and
y
2
(
t
) at any later time
t
.
Note that coordinates
y
i
are measured to the right, from the left wall. It would be useful to first find the
equilibrium state and then define coordinates
x
i
(see below) that measure the displacements away from that state.
Of course, to determine the equilibrium state one needs extra information, including the distance between the two
walls, which we denote by
L
, and the natural (non-extended) lengths of the springs, which we denote by
l
i
for
i
=1
,
2
,
3.
To start analysing the system, let us write down the forces which spring
i
applies on the body (of mass
m
i
)
to its right. The positive direction is to the right (recall that the positions
y
i
(
t
) are measured towards the right).
According to Hooke’s law it is: