Falling Balls 1 Falling Balls 2 Introductory Question Introductory Question Suppose I throw a ball upward into the air. Suppose I throw a ball upward into the air. � After the ball leaves my hand, is there any After the ball leaves my hand, is there any Falling Balls Falling Balls force pushing the ball upward? force pushing the ball upward? Yes Yes A. A. No No B. B. Falling Balls 3 Falling Balls 4 Observations about Falling Balls Observations about Falling Balls 5 Questions about Falling Balls 5 Questions about Falling Balls � When you drop a ball, it When you drop a ball, it � Why does a dropped ball fall downward? Why does a dropped ball fall downward? � � begins at rest, but acquires downward speed begins at rest, but acquires downward speed � Do different balls fall at different rates? Do different balls fall at different rates? � covers more and more distance each second covers more and more distance each second � Would a ball fall differently on the moon? Would a ball fall differently on the moon? � When you tossed a ball straight up, it Wh When you tossed a ball straight up, it Wh d d b ll b ll i h i h i i � Can a ball move upward and still be falling? Can a ball move upward and still be falling? � rises to a certain height rises to a certain height � Does a ball’s horizontal motion affect its fall? Does a ball’s horizontal motion affect its fall? � comes briefly to a stop comes briefly to a stop � begins to descend, much like a dropped ball begins to descend, much like a dropped ball � A thrown ball travels in an arc A thrown ball travels in an arc Falling Balls 5 Falling Balls 6 Question 1 Question 1 Gravity and Weight Gravity and Weight � Why does a dropped ball fall downward? Why does a dropped ball fall downward? � Gravity exerts a Gravity exerts a force force on the ball on the ball � � What is gravity doing to the ball? What is gravity doing to the ball? � That force is the ball’s That force is the ball’s weight weight � Since earth’s gravity produces the ball’s weight, Since earth’s gravity produces the ball’s weight, that weight points toward the earth’s center that weight points toward the earth’s center h h i h i h i i d h d h h’ h’ � The ball’s weight causes it to accelerate toward The ball’s weight causes it to accelerate toward the earth’s center (i.e., downward) the earth’s center (i.e., downward) 1
Falling Balls 7 Falling Balls 8 Question 2 Question 2 Weight and Mass Weight and Mass � Do different balls fall at different rates? Do different balls fall at different rates? � A ball’s weight is proportional to its mass A ball’s weight is proportional to its mass � If different balls have different If different balls have different weights weights and different and different weight/mass = constant weight/mass = constant masses masses, is there any relationship between their , is there any relationship between their � On earth’s surface, On earth’s surface, accelerations as they fall? accelerations as they fall? y weight/mass = weight/mass = 9.8 newtons/kilogram 9.8 newtons/kilogram � is the same for all balls (or other objects) is the same for all balls (or other objects) � is called “acceleration due to gravity” is called “acceleration due to gravity” Falling Balls 9 Falling Balls 10 Acceleration Due to Gravity Acceleration Due to Gravity Clicker Question Clicker Question � Why this strange name? Why this strange name? If we could eliminate air resistance, would a If we could eliminate air resistance, would a � � light sheet of paper and a heavy book fall at light sheet of paper and a heavy book fall at weight/mass → force/mass = acceleration weight/mass → force/mass = acceleration the same rate? the same rate? � Acceleration due to gravity Acceleration due to gravity is is an acceleration! an acceleration! 9.8 newtons 9.8 newtons/kilogram = 9.8 meter/second /kilogram = 9.8 meter/second 2 2 Yes Yes A. A. � On earth’s surface, all falling balls accelerate On earth’s surface, all falling balls accelerate No No downward at 9.8 meter/second 2 2 downward at 9.8 meter/second B. B. � Different balls fall at the same rate! Different balls fall at the same rate! � Falling Balls 11 Falling Balls 12 Question 3 Question 3 Question 4 Question 4 � Would a ball fall differently on the moon? Would a ball fall differently on the moon? � Can a ball move upward and still be falling? Can a ball move upward and still be falling? � Yes! Yes! � How does falling affect a ball’s How does falling affect a ball’s � Moon’s acceleration due to gravity is different! Moon’s acceleration due to gravity is different! � acceleration? acceleration? � velocity? velocity? velocity? velocity? � position? position? 2
Falling Balls 13 Falling Balls 14 A Falling Ball A Falling Ball (Part 1) Falling Downward Falling Downward (Part 1) � A falling ball accelerates downward steadily A falling ball accelerates downward steadily � � Its acceleration is constant and downward Its acceleration is constant and downward � Its velocity increases in the downward direction Its velocity increases in the downward direction � When falling from rest (stationary), its When falling from rest (stationary), its Wh Wh f lli f lli f f ( ( i i ) i ) i � velocity starts at zero and increases downward velocity starts at zero and increases downward � altitude decreases at an ever faster rate altitude decreases at an ever faster rate Falling Balls 15 Falling Balls 16 A Falling Ball A Falling Ball (Part 2) Falling Upward First Falling Upward First (Part 2) � A falling ball can start by heading upward! A falling ball can start by heading upward! � � Its velocity starts in the upward direction Its velocity starts in the upward direction � Its velocity becomes less and less upward Its velocity becomes less and less upward � It � Its altitude increases at an ever slower rate Its altitude increases at an ever slower rate It ltit d in r ltit d in r t n t n r l r l r r t r r t � At some point, its velocity is momentarily zero At some point, its velocity is momentarily zero � Its velocity becomes more and more downward Its velocity becomes more and more downward � Its altitude decreases at ever faster rate Its altitude decreases at ever faster rate Falling Balls 17 Falling Balls 18 Clicker Question Clicker Question Question 5 Question 5 You jump upward from a springboard and You jump upward from a springboard and � Does a ball’s horizontal motion affect its fall? Does a ball’s horizontal motion affect its fall? � dive gracefully into the pool. At the peak of dive gracefully into the pool. At the peak of � Why does a thrown ball travel in an arc? Why does a thrown ball travel in an arc? your jump, your velocity is your jump, your velocity is changing, but your acceleration is constant. changing, but your acceleration is constant. A. A. constant, and your acceleration is constant. constant, and your acceleration is constant. B. B. constant, but your acceleration is changing. constant, but your acceleration is changing. C. C. changing, and your acceleration is changing. changing, and your acceleration is changing. D. D. 3
Falling Balls 19 Falling Balls 20 Throws and Arcs Throws and Arcs Introductory Question (revisited) Introductory Question (revisited) � Gravity only affects only Gravity only affects only Suppose I throw a ball upward into the air. Suppose I throw a ball upward into the air. � the ball’s vertical motion the ball’s vertical motion After the ball leaves my hand, is there any After the ball leaves my hand, is there any � A ball coasts horizontally A ball coasts horizontally force pushing the ball upward? force pushing the ball upward? while falling vertically while falling vertically g g y y Yes Yes A. A. No No B. B. Falling Balls 21 Summary About Falling Balls Summary About Falling Balls � Without gravity, a free ball would coast Without gravity, a free ball would coast � � With gravity, an otherwise free ball With gravity, an otherwise free ball � � experiences its weight, experiences its weight, � accelerates downward, accelerates downward, l l d d d d � and its velocity becomes increasingly downward and its velocity becomes increasingly downward � Whether going up or down, it’s still falling Whether going up or down, it’s still falling � Its horizontal coasting motion is independent of Its horizontal coasting motion is independent of its vertical falling motion its vertical falling motion 4
Recommend
More recommend
