Commensalism is the term you are looking for
Answer:
Oil
Explanation:
Since, unlike oil, source like wind, solar, water etc. come naturally we don't and can't replace them but when the viscosity in oil has been used up it must be change to allow the proper functioning of the machine.
Sirius B is brighter than the sun.
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
