PHYSICSLecture 3Free Fall

Southern Boone County High School

Bill Palmer

Physics-Free FallAll freely falling objects fall at the same

rate-Galileo 1600sNeglecting the effects of airTrue in air or waterGalileo “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 FallWhat if a ball is thrown up?The ball slows down so a is negative.a= -g = -9.80 m/s2

Physics-Free FallThrow a ball upward with a velocity of

20 m/s. Gravity slows the velocity at a rate of

9.80 m/sSo, after 1 sec the ball has slowed from

20 m/s – 9.80 m/s = 10.2 m/sAfter 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 FallWhat happens after three seconds? .4 m/s – 9.80 m/s = - 9.4 m/sNow the ball is going downAt 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 FallThe 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 FallA 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 FallA 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 FallA 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 FallA 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 FallA 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 FallA 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 FallMr. 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 FallMr. 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?

PhysicsComplete 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 MondayTest on Wednesday