Download Chapter 11 Forces

Notes
Newton’s Three Laws of
Motion
Forces
1. Newton’s
First Law states an
object at rest remains at rest and
an object in motion maintains its
velocity unless it experiences an
unbalanced force.
Newton’s First Law
A. Newton’s first law
is sometimes called
the Law of Inertia.
B. Inertia is related to an
object mass
C. Mass is a measure of inertia.
D. An object with a small mass
has less inertia than an object
with a large mass. For,
example a softball has less
mass and less inertia than a
bowling ball does.
Newton’s Second Law
2. Newton’s second law
states the unbalanced
force acting on an object
equals the object’s mass
times its acceleration.
Mathematically-Newton’s 2nd law
A. Newton’s second law, which
describes the relationship
between mass, force, and
acceleration, can be written as
follows.
force = mass x acceleration
f = ma
Unit for force = N (kg x m/s2)
Newton’s
nd
2
Law
B. Newton (N) is a measure of
force
C. Kilogram (kg) is a measure of
mass
D. Meters per second squared
2
(m/s ) is a measure of
acceleration
Newton’s
E. The
nd
2
Law also states
acceleration of an
object is proportional to
the net force on the object
and inversely
proportional to the
object’s mass.
F. The second law can also be
written as follows.
acceleration =
a
=
force
mass
F
m
Unit for acceleration = m/s2
G. The second law also can be
written as follows.
mass = force
acceleration
m = f_
a
unit for mass = kg
Law of Universal Gravitation
3. The Law of Universal
Gravitation states that all
objects in the universe attract
each other through
gravitational force.
A. All matter is affected by
gravity
Gravitational Force
B. Gravitational force increases as mass
increases
C. Gravitational force decreases as
distance increases
D. Gravitational force is small between
objects that have small masses.
Gravitational force
E. Gravitational force is larger
when one or both objects have
larger masses.
F. Universal gravitational equation:
F = m1m2
d2
Free Fall and Weight
4. When gravity is the
only force acting on an
object, the object is
said to be in free fall
Free Fall and Weight
A. Free-fall acceleration near
Earth’s surface is constant; in
the absence of air resistance, all
objects near Earth’s surface
accelerates at the same rate,
regardless of their mass.
B. The force on an object due to gravity
is called its weight
C. Weight equals mass times free-fall
acceleration, this is expressed as
follows
Weight = mass x free-fall acceleration
w = mg
D. Weight due to gravity on
earth is
2
9.8m/s
E. Weight is a force, the SI unit of
weight is the Newton (N).
F. Weight is different from mass.
Mass and weight are easy to confuse.
Although mass and weight are
directly proportional to one another,
they are not the same.
G. Mass is a measure of the amount
of matter in an object.
H. Weight is the gravitational force
an object experiences because of
its mass.
I. The weight of an object depends
on gravity, so a change in an
object’s location will change the
object’s weight.
Free-Fall
J. Weight influences shape;
gravitational force
influences the shapes of
living things.
K. Velocity is constant when
air resistance balances
weight
Newton’s Third Law
5. Newton’s third law states for
every action, there is an equal
and opposite reaction force.
A. Forces always occur in
pairs
B. Force pairs do not act on
the same object
C. Equal forces don’t always have
equal effects
D. Momentum is
calculated by multiplying
an object’s mass by its
velocity.
Law of Conservation of Momentum
• According to the law of conservation
momentum, if objects exert forces
only on each other, their total
momentum is conserved.
• The momentum of an object doesn’t
change unless its mass, velocity, or
both change.
Momentum
E. The SI unit for momentum
is kilograms times meters
per second (kg. m/s).
momentum = mass x velocity
p = mv
Mass = momentum
velocity
m = P
V
Velocity = momentum
mass
V = P
m
Symbols and Units
Momentum (p) = kg x m/s
Mass (m) = kg
Velocity (v) = m/s