1. Chapter 7.2 – Projectile Motion
Set-up a new Cornell Notes Page:
Essential Question: How do we predict the motion of a projectile?
Warm-up question: Where do you have to aim to hit the monkey with the banana? Why?

2. Shoot the Monkey!

3. Now in Slow-Mo!

4. What is a projectile?
A projectile is an object moving in TWO dimensions - Vertical and Horizontal
A projectile is only accelerating in ONE direction – down
ONLY acceleration is from gravity.

5. What is Projectile Motion?
Projectile Motion is a combination of two types of motion:
Horizontal
Motion of a ball rolling freely along a level surface
Horizontal velocity is ALWAYS constant
Vertical
Motion of a freely falling object
Acceleration due to gravity = 9.8 m/s2 down
Vertical component of velocity changes with time

6. What does projectile motion look like?
While a projectile is in the air, what happens to the horizontal velocity?

8. What does projectile motion look like?
While a projectile is in the air, what happens to the horizontal velocity?
While a projectile is in the air, what happens to the vertical velocity?

10. What does projectile motion look like?
While a projectile is in the air, what happens to the horizontal velocity?
While a projectile is in the air, what happens to the vertical velocity?
What is the acceleration of a projectile? Which direction? Constant or changing magnitude?

11. Examples of Projectile Motion
Launching a Cannon ball

12. What does projectile motion look like?
Is the distance a projectile falls vertically affected by its horizontal velocity?
Think about rolling a ball off of a table – does it fall farther down if you roll it faster?
This is the key: The horizontal and vertical motion of a projectile are SEPARATE – they don’t affect each other at all!
BUT – it takes the same amount of time both ways

13. A classic mind-bender: If a bullet is dropped from rest from an elevated position at the same instant that a second bullet is fired horizontally (from the same height), then which bullet will hit the ground first? Assume the bullets behave as projectiles.

14. Bullet Demo

15. How do we predict the motion of a projectile?
We calculate each direction separately!
Horizontal Component
dhorizontal = d0 + ʋ0t + ½ at2
But a = 0! So this reduces to…
dhorizontal = d0 + ʋ0t
Why can’t we use any of the other equations?

16. How do we predict the motion of a projectile?
Vertical Component
dvertical = d0 + ʋ0t + ½ at2
ʋ = ʋ0 + at
ʋ2 = ʋ02 + 2a(d - d0)

17. How do we predict the motion of a projectile?
Vertical – Component
But – what is a? If the position of the ground is 0m, then up is positive, and
a= -9.8m/s2 (called g)
Like this:
Why don’t we ever need
d = d0 + ½(ʋ + ʋ0)t?

18. Homework #1
A stone is thrown horizontally at 7.5 m/s from a cliff 87 m high. How far from the base of the cliff does the stone strike the ground?