Projectile Motion

Projectiles What is a projectile? Projectile: Object moving through space upon which the only force acting is gravity.

Gravity How does gravity affect you? Gravity is all “downwardness.” There is no “sidewayness” to it.

Projectile Motion Projectile motion has two independent components: Vertical motion Horizontal motion Do they affect one another? No! Because the two components are independent of each other, we can separate them for calculations.

Horizontal Motion Projectiles have a constant horizontal velocity in the absence of horizontal force. Ex. When a ball rolls on a table, it rolls with a constant velocity. There is not horizontal force acting on the ball, so there is no horizontal acceleration. Horizontal velocity is constant.

Vertical Motion The vertical component of projectile motion is not constant. It is affected by gravity at 10 m/s2. Due to the force of gravity, a projectile will accelerate as it falls.

The ball is in free fall vertically and moves at a constant speed horizontally (check out the grid lines: horizontal vs. vertical)

Projectile Motion Notice the shape of path! What is the name of this shape? Parabola: When we combine the motion in the horizontal and vertical directions, projectiles move in a shape called a parabola.

What happens when a projectile like a cannonball is shot at an upward angle? Because of gravity, the cannonball follows a curved path and finally hits the ground.

What would happen if gravity didn’t affect the cannonball? In the absence of gravity, the cannonball would follow a straight line path. The vertical distance the cannonball travels (how far above the ground it is) is the same distance the cannonball would fall if it were dropped from rest and allowed to fall for the same amount of time.

Does the launch angle matter? The launch angle does matter! At a steeper angle, there is greater vertical component to velocity, so the projectile travels higher. Since the horizontal component is less, the horizontal range is less.

How are launch angles related? The same horizontal range is obtained for two different projection angles if the angles add up to 90 degrees. The smaller angle will remain in the air for a shorter amount of time. The launch angle that has the greatest horizontal range is 45 degrees.

What about air resistance? When air resistance is significant, the range of a projectile is diminished and the path is not a true parabola.