Free Fall
Lab Physics
Created by K.Rick
Essential Question:
What may be gained by
understanding the effect that gravity
has on motion?
• Because of gravity, objects accelerate
as they fall to the ground.
• A free-falling object is an object
falling under the sole influence of
gravity.
a. There is no air resistance acting
on a free-falling object.
b. A space without air resistance is
called a vacuum.
• The acceleration due to gravity
on earth at sea level in a
vacuum is 9.81 m/s2 .
a. Acceleration due to
gravity is represented by
the letter g.
b. So, g = 9.81
2
m/s
• Air resistance will cause
falling objects to accelerate
at a slower rate than 9.81
m/s2.
Because of air
resistance, falling
objects will reach a
final speed. This is
called terminal
velocity.
Motion Diagrams
for Free-Falling Objects
What is the initial speed of an object that
is dropped?
0
Draw a motion diagram for a dropped
falling object for the first 3 seconds of
motion. Start with time = 0. Generally
down is considered the negative
direction (but it doesn’t have to be).
t = 0, v = 0
t = 1s, v = -9.81 m/s
t = 2s, v = -19.62
m/s
t = 3s, v = -29.43 m/s
An object is tossed upward with a velocity
of 29.43 m/s. Draw a motion diagram for
the object for the first 6 seconds of motion.
Start with time = 0.
t = 2s,
v = 9.81 m/s
t = 3s, v = 0
t = 4s,
v = -9.81 m/s
t = 1s,
v = 19.62 m/s
t = 5s,
v = -19.62 m/s
t = 0s,
v = 29.43 m/s
t = 6s,
v = -29.43 m/s
Because of gravity, objects will
slow down as they go up and
increase speed as they come
back down.
The total amount of time in the
air is called the hang time.
Key Concepts:
• For all problems assume it takes place
on Earth at sea level in a vacuum
unless stated otherwise. This means
g = 9.81 m/s2.
• Dropped, vi = 0
• At maximum height, v = 0
• Acceleration is usually made negative
since gravity pulls down.
How Fast?
• To find the instantaneous speed of an
object in free fall use the following
equation:
•V = g t
Check Your Understanding :
• What would be the speedometer reading on a falling rock 4.5
seconds after it drops from rest?
• How about 8 seconds?
How far?
d = ½ g (t2)
Find the distance
an object will fall
after 8 seconds of
free fall.
Time (s)
Distance (m)
0
1
2
3
4
5
0
5
20
45
80
125
How long?
d = ½ g (t2)
T= 2d/g
How long has this
skydiver free fallen
if he falls for 80
meters?
Check Yourself :
• An object is dropped from rest and falls freely. After 6
seconds, calculate its instantaneous speed and distance fallen.
Instan. Speed
Distance
V=gt
d = ½ g t2
V= 10 m/s2 * 6s
d = ½ 10m/s2 * 6s2
V = 60 m/s
d = 180 m
Double Check Yourself :
• An object is dropped from rest and falls freely. After 8
seconds, calculate its instantaneous speed and distance fallen.
Instan. Speed
Distance
V=gt
d = ½ g t2
V= 10
m/s2
V = 80 m/s
* 8s
d = ½ 10m/s2 * 8s2
d = 320 m
More Practice
• An object falls a distance of 125m. What is its instantaneous
speed just before it hits the ground?
(hint: find t then find v)
FYI: DaVinci’s Parachute
His design
is highly
functional!
• This is DaVinci’s 1493
parachute design
• This is the
modern reproduction
of his sketch.