PHYSICS Lecture 3 Free Fall Southern Boone County

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 1600 s ® 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 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 = -9. 80 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 = - 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 long does the ball stay in the air? (hint) time to rise is same as time to fall 2. 3 s going up so 2. 3 s + 2. 3 s = 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/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 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