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Ch.3.3 Projectile Motion

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Projectile Motion

  • Projectile motion: the motion of an object which is launched into the air and subjected to gravity

We use vectors to describe the motion, and we break the vectors into horizontal and vertical components to simplify the motion

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Components Simplify Projectile Motion

θ

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Consider the following…

  • A launcher is set to shoot one marble forward (like a projectile) and drop another marble from the same height at the same time. Which marble will hit the ground first?

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Projectile Motion Demo

  • The marbles hit at the same time! Why?
  • Gravity causes both marbles drop at the same rate

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Video-Projectile Motion

  • Projectile motion explained by a college professor – take a look!

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Components Simplify Projectile Motion

This leads us to a very important conclusion:

  • Horizontal and vertical components can be treated separately

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  • Projectile motion is free fall with an initial horizontal velocity

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Video-Mythbusters

  • Is this true in all cases? Is this true in extreme cases?
  • Mythbusters scientists shot a bullet and dropped a bullet at the same time and observed whether or not they hit the ground at the same time.

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Formulas for Projectiles Launched Horizontally

Vertical Motion of a Projectile that Falls From Rest

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Horizontal Motion of a Projectile

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Textbook Example pg.98

The Royal Gorge Bridge in Colorado rises 321 m above the Arkansas River. Suppose you kick a rock horizontally off the bridge. The magnitude of the rock’s horizontal displacement is 45.0 m. Find the speed at which the rock was kicked.

D

U

F

A

∆y = -321 m ∆x = 45.0 m

ay = -9.81 m/s2 vx = ?

∆t = ?

= 2(-321 m) = 8.09 s = ∆t

-9.81m/s2

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Textbook Example pg.98

The Royal Gorge Bridge in Colorado rises 321 m above the Arkansas River. Suppose you kick a rock horizontally off the bridge. The magnitude of the rock’s horizontal displacement is 45.0 m. Find the speed at which the rock was kicked.

D

U

F

A

∆y = -321 m ∆x = 45.0 m

ay = -9.81 m/s2 vx = ?

∆t = 8.09 s

= 45 m = 5.56 m/s

8.09 s

S

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Preview of AP Physics: �Objects Launched at an Angle

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Homework

Pg.99 #1-4