# Does a rigid rod store any energy?

1. Mar 8, 2015

### jcap

I presume that a rod can be modelled as a spring with spring constant k and compression x.

The potential energy in a spring is given by:
$$E = \frac{1}{2}kx^2$$
If the spring is in equilibrium with an applied force F then we have:
$$F = k x$$
Thus the potential energy in the spring in terms of the force is:
$$E = \frac{1}{2}\frac{F^2}{k}$$
Thus if we have a very stiff spring so that $k\rightarrow\infty$ then the energy stored in the spring tends to zero for any force applied to the spring.

Is that correct?

2. Mar 8, 2015

Chet

3. Mar 8, 2015

### CWatters

Perhaps confirm it by looking at the work done by the applied force as it compresses the spring?

work = force * displacement

If the spring is very stiff the displacement is going to approach zero.