can change the direction of motion but never change the speed. For moving objects, the quantity of work/time is calculated as distance/time, or velocity. Thus, at any instant, the rate of the work done by a force (measured in joules/second, or watts ) is the scalar product of the force (a vector), and the velocity vector of the point of application. This scalar product of force and velocity is classified as instantaneous power . Just as velocities may be integrated over time to obtain a total distance, by the fundamental theorem of calculus , the total work along a path is similarly the time-integral of instantaneous power applied along the trajectory of the point of application. [ 4 ] Work is the result of a force on a point that moves through a distance. As the point moves, it follows a curve X , with a velocity v , at each instant. The small amount of work δW that occurs over an instant of time dt is calculated as where the F.v is the power over the instant dt . The sum of these small amounts of work over the trajectory of the point yields the work, where C is the trajectory from x (t 1 ) to x (t 2 ). This integral is computed along the trajectory of the particle, and is therefore said to be path dependent . If the force is always directed along this line, and the magnitude of the force is F , then