Chapter 19: When Things Move with Constant Velocity and Acceleration

A projectile is an example of a body that simultaneously moves in both the x and y direction. When things move, they can travel in a circle (planets orbiting the sun), travel in a horizontal direction (Cheetah chasing a prey), or move vertically (autumn leaves falling). They can also move in two dimensions—horizontal and vertical (human performing a long jump). A body thrown or launched into the air and subjected to gravitational force (gravity) is called a projectile (Serway & Faughn, 2015). Gravity accelerates the body in the vertical direction and causes the body to follow a parabolic trajectory in the absence of air resistance. The vertical velocity is solely influenced by gravity, causing velocity to change by 9.8 m/s each second. A projectile does not experience a force in the horizontal direction. Its inertia propels it once the body is launched. In the absence of air resistance, the horizontal velocity is considered constant (no acceleration) and this premise is assumed in this lesson plan. The time of flight for an object that moves in both the vertical and horizontal dimensions is always equal and this knowledge can be used to solve projectile problems since it provides a common variable that is constant in both dimensions (Mader & Winn, 2007, p. 109).