Projectile Motion Projectile Motion 9 27

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Projectile Motion Projectile Motion 9 27 Powered By Docstoc
					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
• http://www.youtube.com/watch?v=D9wQVI
  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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