The average vibration of molecules in an object is measured by temperature.

Here's why:

* Temperature is a measure of the average kinetic energy of the molecules in a substance. Kinetic energy is the energy of motion.

* Molecules are constantly in motion, vibrating, rotating, and translating. The higher the temperature, the faster these movements.

* Increased vibration, rotation, and translation lead to a higher average kinetic energy. This is directly reflected in the object's temperature.

So, while we can't directly "see" the vibrations of individual molecules, we can measure their average kinetic energy through temperature, which gives us a good indication of how much those molecules are moving around.