Projectile Motion

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Projectile Motion
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Fact or Fiction

• For a fastball to travel at 90 mph, the pitchers
  hand (or fingers) must be moving at 90 mph when
  the ball is released
• The moon is constantly falling towards Earth
• A coin dropped off a cliff will reach the ground
  before another coin thrown horizontally from the
  cliff at the same height.

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Projectile

• Object that is launched by a force and continues
  to move by its own inertia
• Only force acting on object is gravity
• Trajectory- the path of a projectile (parabola)

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Projectile Motion

• Horizontal (x) and Vertical (y) components are
  independent of each other
• No force acts horizontally Horizontal motion is
  constant.
• Force of gravity acts vertically vertical motion
  is accelerated

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What does this mean?

• Objects propelled horizontally also fall
  vertically at a rate of 9.8 m/s2 (No matter how
  hard object is thrown)
• Horizontally launched object and one that is
  dropped

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Rolling Ball off Table

• If we push the ball harder, giving it greater
  ___________ velocity as it rolls off the table,
  the ball takes _____ time to fall to the floor.
  Draw the new trajectory

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Rolling Ball off Table
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Projectiles have 2 velocities- Horizontal and
Vertical!

•  
• Force of gravity only acts vertically
• Vertical Velocity (Vy) - Force of gravity
  accelerates objects vertically at a rate of 10
  m/s2 downward. (So in the vertical direction
  the ball slows down on the way up and speeds back
  up on the way down by 10 m/s every second)
• Horizontal Velocity (Vx)
• In absence of air resistance, projectile
  maintains initial horizontal velocity it was
  given. (Inertia) 
• Vx is constant!
• Vix Vx constant
• Vx dx/t
•  

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Objects that are thrown horizontally

• only one factor determines the time in air. 
• Object's initial height (dy)
• t in air

dy
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Objects that are thrown horizontally

• To find the maximum range (dx) or horizontal
  displacement use the formula
• dx vxt

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Ex. A stone is thrown horizontally at 7.5 m/s
from a cliff that is 68.4 m high. How far from
the base of the cliff does the stone land?

• Draw a diagram of this situation
• Break up information into x and y!
• 27.8 m from the base of the cliff

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Ex. A baseball is thrown horizontally with a
velocity of 44 m/s. It travels a horizontal
distance of 18 m to the plate before it is caught.

• A. How long does the ball stay in the air?
• B. How far does the ball drop during its flight?
• A 0.41 s B 0.82 m

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What will happen if a pilot drops a package when
the plane is directly over the target?
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The trajectory of a projectile launched upwards
looks like...
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Monkey and the tranquilizer gun

• A scientist needs to shoot the monkey with a
  tranquilizer gun, but he knows that as soon as he
  shoots the gun, the monkey will let go of the
  tree and fall to the ground. Should he aim
  (above, beneath, or straight at) the monkey?
• Monkey the Hunter

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Thrown at monkey with slow speed
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Thrown at monkey with fast speed
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Does the moon fall in the sky?
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Satellites are

• Projectiles that fall around Earth
• The moon is a satellite
• Geosynchronous orbits match the Earths spin

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Show what you know

• 1. A projectiles motion is...
• a. linear.
• b. one-dimensional.
• c. two-dimensional.
• d. three-dimensional.
• 2. A projectiles horizontal motion is...
• a. uniform (constant).
• b. accelerated.
• c. absent.

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Show what you know

• 3. The vertical component of a projectiles
  motion is...
• a. uniform (constant).
• b. accelerated.
• c. absent.
• 4. A boy is riding a skateboard along a smooth,
  flat street. If he jumps straight up off the
  board, he will land...
• a. in front of the board.
• b. behind the board.
• c. on the board.