Kinematics is the branch of mechanics concerned with the phenomena of motion without reference to mass or forces. In kinematics we deal with distance and time, which are scalar quantities, and with velocity and acceleration, which are vector quantities.

Often we have to consider the combination of velocities in different directions. Consider a ship sailing due E at a velocity x, and carried N by a current with velocity y. The resultant velocity z can be found by using a diagram where the arrows represent the velocities in both magnitude and direction or by trigonometry. Velocities can be resolved in a similar way. (By resolving is meant simply finding the components in different directions.)