Projectile Motion

Instructional Objectives:

• Students will be able to:– Define Projectile Motion– Distinguish between the different types of

projectile motion– Apply the concept to a toy catapult and

measure its velocity

What is Projectile Motion?

A projectile, once projected, continues inmotion by its own inertia and is influencedonly by the downward force of gravity.

Projectile Motion• Projectile Motion – objects that are thrown

or launched into the air and are subject to gravity

• Use of components avoid vector multiplication

• Components simplify projectile motion

• Projectile motion is free fall with an initial horizontal velocity

An object projected horizontally will reach the ground in the same time as an object dropped vertically.

No matter how large the horizontal velocity is, the downward pull of gravity is always the same.

Examples of Projectile Motion

• Launching a Cannon ball

• Projectiles follow parabolic motion

The path of a projectile is called its trajectory. The trajectory of a projectile in free fall is a parabola.

Types of Projectile Motion

• Horizontal– Motion of a ball rolling freely along a

level surface– Horizontal velocity is ALWAYS constant

• Vertical– Motion of a freely falling object– Force due to gravity– Vertical component of velocity changes

with time• Parabolic

– Path traced by an object accelerating only in the vertical direction while moving at constant horizontal velocity

Horizontal Projectiles

Δy = ½gΔt2

Δx = vxΔt

g = 9.81 m/s2

vx

Δy

Δx

Δt

The Royal Gorge in Colorado rises 321 m above the Arkansas River. Suppose you kick a little rock horizontally off the bridge. The rock hits the water such that the magnitude of its horizontal displacement is 45.0 m. Find the speed at which the rock was kicked.