In the previous unit, we studied simple straight-line motion (linear motion). We distinguished between motion with constant velocity, such as a bowling ball rolling horizontally, and accelerated motion, such as an object falling vertically projectile motion under the influence of gravity. Now we extend these ideas to nonlinear motion- motion along a curved path. Throw a baseball and the path it follows is a curve. This curve is a combination of constant velocity horizontal motion and accelerated vertical motion. We’ll see that the velocity of a thrown ball at any instant has two independent “components” of motion- what happens horizontally is not affected by what happens vertically (Prentice Hall Conceptual Physics-Paul Hewitt)