SRP revolves around the idea that electromagnetic waves are mass-less, but exhibit mass-like properties. The photons in light emitted from the Sun move at the speed of light and have momentum. Because they have momentum, when they hit other objects, they transfer momentum to that object, giving it a boost in velocity.
The flow of electric charges that is observed in electrolytes
Thrust is the force which moves the rocket through the air, and through space
Specific impulse is the change in momentum per unit mass for rocket fuels
The difference between the rocket speed and the propellant speed is called the exhaust speed