Transcript forces - Cloudfront.net

Lecture series from Conceptual Physics 8th ed.
Newton’s First Law of Motion (56)
Inertia is the tendency of
things to resist motion.
Alias: The law of
Push the card out of the
way quickly. The coin
resists being pushed.
Pull quickly on the
bottom string and the ball
resists being moved.
Slam the hammer down and the
head resists being stopped…
i.e. keeps moving.
In Newton’s words….his first law:
Every object continues in its state of rest, or of uniform
motion in a straight line, unless it is compelled to
change that state by forces impressed upon it.
INERTIA
Let’s define mass and force:
MASS= A measure of an object’s inertia, quantity of matter.
A “weightless” object
has mass. It resists
being moved.
FORCE= A push or pull.
Weight is a force.
Mass is measured in units of kilograms, kg
Answer p. 60
Newton’s Second Law of Motion
p60
The acceleration of an object is directly
proportional to the net force acting on the object,
is in the direction of the net force, and is inversely
proportional to the mass of the object. (p60)
a=
F
m
The unit of force is the Newton, N.
Forces are vectors.
Note: equilibrium exists!
When Acceleration Is Zero – Equilibrium p62
P 64
Static vs Sliding friction.
FRICTION
When Acceleration Is g – Free Fall p66
For fig 4-13, note that
p 67
F = 2F = g
m
2m
Terminal velocity
The person’s weight --
F = mg
As velocity increases so does air
resistance, R.
R mg
Mg - R
So, a = m
R
v
t
mg
Newton’s Third Law of Motion p70
Whenever one object exerts a force on a
second object, the second object exerts an
equal an opposite force on the first.
Action
Reaction
P 72
Because masses
are different.
The forces are equal.
Why aren’t the
accelerations equal?
The bullet -The gun --
a
a
=
=
F
F
m
mThe End