PHYSICS%20Lecture%203%20Free%20Fall

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PHYSICSLecture 3Free Fall

• Southern Boone County High School
• Bill Palmer

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Physics-Free Fall

• All freely falling objects fall at the same
  rate-Galileo 1600s
• Neglecting the effects of air
• True in air or water
• Galileo Diluted gravity by rolling things down
  ramps (sound familiar?)
• Leaning Tower of Pisa

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Physics-Free Fall

• gAcceleration due to gravity
• Slight differences at various spots on earth due
  to due to uneven distribution of mass over
  earths surface
• Think of g over a iron mine vs. g over ocean
• g9.80 m/s2
• For each second an object falls the downward
  velocity increases by 9.80 m/s

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Physics-Free Fall

• What if a ball is thrown up?
• The ball slows down so a is negative.
• a -g -9.80 m/s2

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Physics-Free Fall

• Throw a ball upward with a velocity of 20 m/s.
• Gravity slows the velocity at a rate of 9.80 m/s
• So, after 1 sec the ball has slowed from 20 m/s
  9.80 m/s 10.2 m/s
• After 2 sec the ball has slowed another 9.80 m/s
  or 10.2 m/s 9.8 m/s .4 m/s

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Physics-Free Fall

• What happens after three seconds?
• .4 m/s 9.80 m/s - 9.4 m/s
• Now the ball is going down
• At 4 seconds the ball is moving down at 9.4 m/s
  plus another 9.80 m/s 19.2 m/s
• At about 2 sec, the balls velocity is 0

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Physics-Free Fall

• The Demon Drop is a ride at an amusement park
  where a car falls freely for 1.5 sec after
  starting from rest.
• What is its velocity at the end of 1.5 s?
• How far did it fall?

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Physics-Free Fall

• A brick is dropped from a high scaffold.
• What is its velocity after 4.0 s?
• How far does the brick fall in this time?

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Physics-Free Fall

• A brick is dropped from a high scaffold.
• What is its velocity after 4.0 s?
• How far does the brick fall in this time?
• Answer - 39 m/s
• Answer -78 m (downward)

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Physics-Free Fall

• A tennis ball is thrown straight up with an
  initial speed of 22.5 m/s. It is caught at the
  same distance above ground.
• How high did the ball rise?
• How long does the ball stay in the air? (hint)
  time to rise is same as time to fall

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Physics-Free Fall

• A tennis ball is thrown straight up with an
  initial speed of 22.5 m/s. It is caught at the
  same distance above ground.
• How high did the ball rise? A25.8 m
• How long does the ball stay in the air? (hint)
  time to rise is same as time to fall
• 2.3s going up so 2.3s 2.3s 4.6 s total

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Physics-Free Fall

• A spaceship far from any star or plant
  accelerates uniformly from 65.0 m/s to 162 m/s in
  10.0 sec. How far does it move?

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Physics-Free Fall

• A spaceship far from any star or plant
  accelerates uniformly from 65.0 m/s to 162 m/s in
  10.0 sec. How far does it move?
• Answer 1.14 x 103 m

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Physics-Free Fall

• In English system, g equals 32 ft/s2
• Try these problems

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Physics-Free Fall

• Mr. Palmer takes some students rock climbing.
• Ditzy Nicole is watching from the top of a cliff.
  She slips and falls of the cliff and her body
  crashes into the ground directly below 4.6 s
  later.
• How high was the cliff?
• How fast was she going when she hit the ground?
  (f/s and m/h)

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Physics-Free Fall

• Mr. Palmer takes some students to a pit cave.
  They have a 600 f rope. To find out if their rope
  is long enough they throw a rock into the cave
  and watch it hit the bottom (why dont they just
  listen?) The rock takes 3.5 seconds to hit the
  bottom. Is the rope long enough?

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Physics

• Complete the following 10 problems page 107-115
  33, 38, 44, 47, 54, 57, 62, 66, 70, 76.
• Critical thinking problemsgtgtgtwork in teams of
  two. Problems 77, 78, 79
• Review these on Monday
• Test on Wednesday