A wall located outside the cell membrane provides the cell support, and protection against mechanical stress or damage from osmotic rupture and lysis. The major component of the bacterial cell wall is peptidoglycan or murein. This rigid structure of peptidoglycan, specific only to prokaryotes, gives the cell shape and surrounds the cytoplasmic membrane.
The organ that responds to stimuli with vibrations is the eardrum.
Velocity can vary as long there is specific direction (displacement)
Speed has no direction therefore change in speed is not necessary the velocity...
Velocity is also in a specified direction