momentum (p) - A measure of the motion of a body equal to the product of its mass and velocity. Also called linear momentum. Impetus of a physical object in motion.

Momentum is a vector. That means, of course, that momentum is a quantity that has a magnitude, or size, and a direction.

•The principle of conservation of momentum states that the total amount of momentum of all the things in the universe will never change. One of the consequences of this is that the centre of mass of any system of objects will always continue with the same velocity unless acted on by a force outside the system.

•Since momentum is a vector quantity it has direction. Thus, when a gun is fired, although overall movement has increased compared to before the shot was fired, the momentum of the bullet in one direction is equal in magnitude, but opposite in sign, to the momentum of the gun in the other direction. These then sum to zero which is equal to the zero momentum that was present before either the gun or the bullet was moving.

+mv-mv

Thrust is the rate of change of momentum. Therefore just divide the momentum by the time to work out thrust.