Physics 101: Lecture 5, Pg 1
Free Fall and Apparent Weight
Physics 101:
Lecture 05
Today’s lecture will cover
Textbook Sections 4.3,4.5
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Exam 1 is Feb 27.
Exam I

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Physics 101: Lecture 5, Pg 2
Review from Lecture 4
•
Constant Acceleration Equations of Motion
x = x
0
+ v
0
t + 1/2 at
2
v = v
0
+ at
v
2
= v
0
2
+ 2a(x-x
0
)
•
S
F = m a
–
Draw Free Body Diagram
–
Write down equations (which variables do
you know, which don’t you know?)
–
Solve
•
Today: look at Gravity as force

Physics 101: Lecture 5, Pg 3
Free Fall
Only force acting on object is GRAVITY
Newton’s 2
nd
Law
S
F
y
= ma
y
Force is
Weight = mg
(near surface of earth)
»
S
F
y
= ma
y
» -mg = ma
y
» a
y
= -g
(- sign tells us it is in
–
y direction or down).
Acceleration is
ALWAYS
g downwards
Position may be positive, zero or negative
Velocity may be positive, zero or negative
Acceleration is always g downwards
y
x
y = y
0
+ v
y0
t - 1/2 gt
2
v
y
= v
y0
- gt
v
y
2
= v
y0
2
- 2g(y-y
0
)

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