Falling Objects
2.3 pp. 60-65
Mr. Richter
Agenda
 Warm-Up
 Review HW p. 58 #4-6
 Questions about the Lab?
 Intro to Free Fall
 Notes:
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Free Fall
Velocity During Free Fall
Acceleration During Free Fall
Problem Solving w/ Free Fall
Objectives: We Will Be Able To…
 Relate the motion of an object in free fall to motion with
constant acceleration.
 Calculate displacement, velocity, and time at various points
in the motion of an object in free fall.
 Compare the motions of different objects in free fall.
Warm-Up:
 Mr. Richter throws his green ball up in the air and then
catches it.
 Sketch the Position vs. Time Graph and Velocity vs. Time
Graph of the motion of the ball.
Free Fall
Free Fall
 If a piece of paper and a ball bearing are dropped from the
same place, will they fall at the same rate? Why or why not?
 Discuss at your table and we will discuss as a class in a
minute.
Free Fall
 Objects dropped near the
surface of a planet fall at
the same rate.
 REGARDLESS OF MASS!
 This is only true in the
absence of air resistance
(friction). In a vacuum.
Free Fall
Free Fall
 In the picture, the distance
the objects fall each instant
is increasing.
 So the objects must be
accelerating.
 This is the acceleration due
to gravity.
 On Earth, g = 9.81 m/s2
Velocity and Acceleration in Free
Fall
Velocity and Acceleration in Free Fall
 Once something is released (thrown,
dropped, etc.), it immediately starts
experiencing the acceleration due to
gravity.
 Any positive initial velocity is starting to
diminish.
 Once there is no more positive velocity,
the velocity of the object becomes
increasingly negative.
Velocity and Acceleration in Free Fall
 Consider a ball thrown upward with an
initial velocity of +19. 62 m/s
Time (sec)
Velocity (m/s)
0
1
2
19.62
9.81
0
3
-9.81
4
-19.62
Velocity and Acceleration in Free Fall
 Objects with initial positive velocity in free fall have VvT
graphs that look something like this:
Velocity and Acceleration in Free Fall
 Important concepts that play a role in problem solving:
 If an object is propelled upward, v = 0 at the object’s highest
point (peak).
 If an object is propelled from and returned to the same
point:
 its time to reach its peak is exactly half the time it takes to
complete the round trip.
 v1 = - vf (initial and final speeds are equal and opposite)
 Δy = 0
Problem Solving with Free Fall
Problem Solving
 All of the formulas on p. 58 still apply, with two minor
changes:
 Δy instead of Δx (y-axis goes up and down)
 Acceleration a is almost always –g = -9.81 m/s2
Practice Problem (2 steps)
 Jason hits a volleyball so that it
moves with an initial velocity of 6.0
m/s straight upward. If the
volleyball starts from 2.0 m above
the floor, how long will it be in the
air before it strikes the floor?
Wrap-Up: Did we meet our objectives?
 Relate the motion of an object in free fall to motion with
constant acceleration.
 Calculate displacement, velocity, and time at various points
in the motion of an object in free fall.
 Compare the motions of different objects in free fall.
Homework
 p 65 #1-6 Due Monday