Answer the following question given this paragraph: 

The drummer in Figure below is hitting the drumheads with drumsticks. This causes the drumheads to vibrate. The vibrations pass to surrounding air particles and then from one air particle to another in a wave of energy called sound energy . We hear sound when the sound waves reach our ears. Sound energy can travel through air, water, and other substances, but not through empty space. That’s because the energy needs particles of matter to pass it on.


Q: What energy, produced by vibrations, cannot travel through empty space?


A:
sound