The thing bringing energy to the system is called the excitor and the thing that vibrates is excited.
The excited thing can be a resonator, a concept we will develop shortly.
In carbon dioxide gas
where the forces between distant molecules are relatively weak we find sound
moves slowly at 259m/s. Of the 118 common elements, 63 are metals. That
accounts for a wide range of physical properties, and more so if we allow alloys.
Most metals are elastic, hard, dense, and acoustically very conductive.