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?)  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/s 2  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 = m/s 2

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 = 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 10 3 m

Physics-Free Fall  In English system, g equals 32 ft/s 2  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 : 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