momentum

Product of the mass of a body and its velocity. If the mass of a body is m kilograms and its velocity is v m s⁻¹, then its momentum is given by: momentum = mv. Its unit is the kilogram metre-per-second (kg m s⁻¹) or the newton second. The momentum of a body does not change unless a resultant or unbalanced force acts on that body (see Newton's laws of motion).

According to Newton's second law of motion, the magnitude of a resultant force F equals the rate of change of momentum brought about by its action, or: F = (mv – mu)/t where mu is the initial momentum of the body, mv is its final momentum, and t is the time in seconds over which the force acts. The change in momentum, or impulse, produced can therefore be expressed as: impulse = mv – mu = Ft. The law of conservation of momentum is one of the fundamental concepts of classical physics. It states that the total momentum of all bodies in a closed system is constant and unaffected by processes occurring within the system. The angular momentum of an orbiting or rotating body of mass m travelling at a velocity v in a circular orbit of radius R is expressed as mvR. Angular momentum is conserved, and should any of the values alter (such as the radius of orbit), the other values (such as the velocity) will compensate to preserve the value of angular momentum, and that lost by one component is passed to another.