# Projectile Motion Projectile Motion 9 27

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```					Projectile Motion
9/27/11
Bellwork
•   3 ways to accelerate:
•   - Speeding up (gas pedal)
•   - Slowing down (brake pedal)
•   - Turning (steering wheel)
Throwing a ball in the air
• On the way up:    • velocity decreases
• acceleration stays the
same.
• At the top of the • velocity zero
throw:            • acceleration stays the
same.
• On the way down: • velocity increases
• acceleration stays the
same.
Throwing a ball in the air
• The velocity changes.
• The acceleration is constant, it stays
the same 9.81 m/s/s throughout the
flight.
Projectiles
• Projectile are objects where gravity and
air resistance are the only forces acting
• The force of gravity does not affect the
horizontal component of motion
• A projectile’s horizontal component is
independent of the vertical component
• Projectiles travel with a parabolic
trajectory
Mythbusters
• Dropped vs. Fired Bullet
• http://dsc.discovery.com/videos/mythbuste
rs-dropped-vs-fired-bullet.html
EdKh8
Air Resistance
• Air Resistance: A force of friction that
acts on an object moving through the air
• For projectile motion we will neglect or
assume that air resistance is extremely
small
Horizontal    Vertical
Motion        Motion

Force             No      Yes, the force of
gravity acts
downward

Acceleration         No            Yes
"g" is
downward at
9.81 m/s/s

Velocity        Constant      Changing
(by 9.81 m/s
each second)
Projectile
• What happens to a projectile’s
horizontal and vertical velocity?
• What happens to a projectile’s
horizontal and vertical displacement?
• Example: An object with a initial
horizontal velocity of 20 m/s to the right
and vertical velocity of 0 m/s.
Velocity
Time        Horizontal      Vertical
Velocity        Velocity

0s   20 m/s, right       0 m/s
1s   20 m/s, right   10 m/s, down
2s   20 m/s, right   20 m/s, down
3s   20 m/s, right   30 m/s, down
4s   20 m/s, right   40 m/s, down
5s   20 m/s, right   50 m/s, down
Displacement
Time         Horizontal      Vertical
Displacement    Displacement

0s      0 m, right        0m
1s     20 m, right     5 m, down
2s     40 m, right     20 m, down
3s     60 m, right     45 m, down
4s     80 m, right     80 m, down
5s     100 m, right   125 m, down
A falling object
A falling
object
Projectile Animation
• http://ngsir.netfirms.com/englishhtm/Throw
ABall.htm
Projectile Motion
9/28/11
Components
• Component: the projection of a vector
quantity along a perpendicular axis
Components
Horizontal
• Right = +x
• Left = -x
Vertical
• Up = +y
• Down = -y
Projectile Quantities
• Displacement (m)
dx = horizontal displacement
dy = vertical displacement
• Velocity (m/s)
vx = horizontal velocity
vy = vertical velocity
Projectile Quantities
• Acceleration
ax = 0 m/s2 (no horizontal accel.)
ay = -9.81 m/s2 or “g”
• Time (s)
t = time
does not depend on direction (scalar)
is the same for horizontal and vertical
components
Projectile Problems
1. Draw a sketch of the problem to
determine horizontal and vertical
components
2. Use a T-Chart to organize the problem
3. Time (often needed to be solved for
1st) is a scalar, it is the same for the
horizontal and vertical components
Formula Cards
• Component axis
• Projectile (horizontal)
• Projectile (vertical)
Homework
• Example of velocity vectors of an
object going up and down
• Example of projectile motion problem

```
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