Similar to any moving object, once it is moving, it doesn't need anything to "propel" it. It will just continue moving on its own, since that's its natural tendency.
Nothing propels it at all. It actually always goes that fast, even from its creation. To explain it to you mathematically would require the use of 4-D tensor products, so I won't bother with that here. Suffice it to say, that is one of the postulates of Einstein's general relativity. Light always travels at the same speed in any reference frame.
A compressed C02 tank or High Pressure Air tank propels the paintball.
The propeller.
It propels.
Propels it (moves it)
Air
A jet engine usually propels an airplane. The jet engine propels the plane by ejecting extremely hot gasses out the back of the engines. Another way is by using huge fans to suck in air and blow it out the back.
Pseudostratified ciliated columnar epithelial tissue propels substances across surfaces.
It propels it forward in the water.
energy
energy
The engines propel the airplanes.