Molecules inside a solid are not stationary. They are in continuous motion, although it's a very different kind of motion compared to liquids and gases.

Here's why:

* Vibrational Motion: The molecules in a solid vibrate back and forth around fixed positions. These vibrations are very rapid, even at room temperature.

* Limited Translational Motion: While molecules in solids cannot move freely like in liquids or gases, they do exhibit a very small amount of translational motion. This means they can slightly shift their positions, though they remain largely confined to their lattice structure.

* Temperature and Motion: The amount of vibrational and translational motion increases with temperature. This is why solids expand when heated – the increased motion leads to greater spacing between molecules.

So, while molecules in a solid are not "running around" like in a gas, they are still in constant motion, albeit a much more restricted and confined motion compared to other states of matter.