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PHYSICS Lecture 3 Free Fall. Southern Boone County High School Bill Palmer. 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?)
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PHYSICSLecture 3Free Fall Southern Boone County High School Bill Palmer
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
Physics-Free Fall • g=Acceleration due to gravity • Slight differences at various spots on earth due to due to uneven distribution of mass over earth’s surface • Think of g over a iron mine vs. g over ocean • g=9.80 m/s2 • For each second an object falls the downward velocity increases by 9.80 m/s
Physics-Free Fall • What if a ball is thrown up? • The ball slows down so a is negative. • a= -g = -9.80 m/s2
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
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
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?
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?
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)
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
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? A=25.8 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
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?
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
Physics-Free Fall • In English system, g equals 32 ft/s2 • Try these problems:
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)
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 don’t they just listen?) The rock takes 3.5 seconds to hit the bottom. Is the rope long enough?
Physics • Complete the following 10 problems page 107-115: 33, 38, 44, 47, 54, 57, 62, 66, 70, 76. • Critical thinking problems>>>work in teams of two. Problems 77, 78, 79 • Review these on Monday • Test on Wednesday