S-24
I can explain the relationship between weight, gravity, and friction




Define the following terms
A. Weight
B. Gravity
C. Friction
S-25
I can describe different kinds of force.


What does friction normally do to a moving
object?
What would be different in the world if there
was not friction?
Chapter 12
Newton’s Laws
SPS8 Students will determine relationships among force,
mass, and motion.
b. Apply Newton’s three Laws to everyday situations.
c. Relate falling objects to gravitational force.
d. Explain the difference in mass and weight.
12.1 Forces
How do forces affect the motion of an object?
What the four main types of friction?
How do gravity and air resistance affect a falling object?
In what direction does Earth’s gravity act?
12.1 Force
12.1 Forces
How do forces affect the motion of an object?


Force – a push or a pull on an object
Forces cause changes in velocity
 Acceleration - change the objects speed
 or direction

Measured
 Scale, Force Sensor

Unit – measured in Newton’s (N)
 A medium apple will apply a force
of about 1 N
12.1 Force
12.1 Forces
How do forces affect the motion of an object?
 Forces are vectors so they are drawn using arrows
(show magnitude and direction)

Net Force – the overall force acting on an
object after all the forces are combined
 Balanced forces – the net force is zero, no
acceleration
 Unbalanced forces – objects accelerate
12.1 Force
12.1 Forces
What are the four main types of friction


Friction – a force that opposes the motion of
objects that touch as they move past each
other
Four Types
 Static Friction – when objects aren’t moving
 Sliding Friction – when objects are sliding past
each other
12.1 Force
12.1 Forces
What are the four main types of friction
 Rolling Friction – allows movement forward, but
not side to side
 Fluid Friction – when an object is moving through
a fluid
▪ Fluids are liquids or gases – anything that flows
▪ Air resistance is a form of fluid friction
12.1 Force
12.1 Forces
How does gravity and air resistance affect a falling object

Gravity – the force of attraction between any
two objects with mass
 Earth’s gravity points toward the center of the
earth – pulls anything with mass
 Called weight
12.1 Force
12.1 Forces
How does gravity and air resistance affect a falling object
 When an object is falling, two forces act on it
 What do you think they are?
▪ Weight
▪ Air Resistance
Air
Resistance
 Objects will accelerate because of gravity until
they reach a terminal velocity – the speed at which
the weight and air resistance are equal
 For example – terminal
Gravity
speed of a raindrop is about
(Weight)
9 m/s
 Human – 76 m/s
S-26
I can describe different kinds of force.

Name and describe the four types of friction.
S-27
I can describe different kinds of force.

What is the difference between weight and
mass.
12.2 Newton’s 1st and 2nd Laws
of Motion
How does Newton’s first law relate change in motion to a
zero net force?
How does Newton’s second law relate force, mass, and
acceleration?
How are weight and mass related?
12.1 Force
12.2 Newton’s 1st & 2nd Laws
How does Newton’s first law relate change in motion to a zero net force

Newton’s First Law of Motion
 The state of motion of an object does not change
as long as the net force acting on the object is zero
 More commonly
▪ An object at rest remains at rest, and an object in
motion remains in motion, unless acted on by an
outside force.
 Sometimes called the law of inertia
▪ Inertia – the tendency of an object to
resist a change in its motion
12.1 Force
12.2 Newton’s 1st & 2nd Laws
How does Newton’s second law relate force, mass, and acceleration

Newton’s Second Law of Motion
 The acceleration of an object is equal to the net
force acting on it divided by the object’s mass.
F  ma
 F – Force in Newtons
 m – mass in kilograms
 a – acceleration in m/s2
 Always in the same direction as the net force
12.1 Force
12.2 Newton’s 1st & 2nd Laws
How does Newton’s second law relate force, mass, and acceleration
b
c
 Newton’s Second Law of
Motion
– Practice
m
F  ma
Problems a
4000
N

1000
kg
a

4
2
A car with a mass of 1000 kg accelerates
when
s
the traffic light turns green. If the net force on

the car is 4000 N, what is the cars
acceleration?




Equation?
Variables?
Filled In Equation?
Answer?
m  1000 kg
F  4000 N
12.1 Force
12.2 Newton’s 1st & 2nd Laws
How does Newton’s second law relate force, mass, and acceleration
d
c
e
b
 Newton’s Second Law of Motion – Practice
m
ffffff
F

ma
Problems
FAnautomobile
1200
3.0
F with
 kg
400
N
a mass of 1200 kg

s
2
accelerates at a rate of 3.0 m/s2. What is the
force acting on the automobile?




Equation?
Variables?
Filled In Equation?
Answer?
m  1200 kg
a  3.0
ms
2
12.1 Force
12.2 Newton’s 1st & 2nd Laws
How does Newton’s second law relate force, mass, and acceleration
d
e
 Newton’s Second Law of Motion – Practice
m
ffffff
F

ma
Problems

25
N

m
0.5
m

50
kg
A 25 N force accelerates a man on a scooter
2 at
s and
0.5 m/s2. What is the mass of the man
scooter?




Equation?
Variables?
Filled In Equation?
Answer?
F  25 N
a  0.5
ms
2
12.1 Force
12.2 Newton’s 1st & 2nd Laws
How are weight and mass related

Weight and Mass
 Weight the force of gravity acting on an object
 Its mass times acceleration due to gravity
W  mg
 W – Weight in Newtons
 m – mass in kilograms
 g – 9.80 m/s2
12.1 Force
12.2 Newton’s 1st & 2nd Laws
How are weight and mass related

Weight and Mass
 Mass is a measurement of
the inertia of an object
 Weight is a measurement of
the force of gravity acting on
an object
12.3 Newton’s 3rd Law of Motion
and Momentum
What is Newton’s third law of motion?
12.1 Force
12.3 Newton’s 3rd Law
What is Newton’s third law of motion

Newton’s Third Law
 Whenever one object exerts a force on a second
object, the second object exerts an equal and
opposite force on the first object.
 Identify the following action and reaction forces
12.1 Force
12.3 Newton’s 3rd Law
What is Newton’s third law of motion

Newton’s Third Law
 Action-Reaction pairs can cause motion
 The donkey pushes on the ground, the ground
pushes the donkey forward
 Does the donkey push the ground backward?
 Action-Reaction pairs don’t cancel
 They don’t act on the same objects
12.4 Universal Forces
What are the four fundamental forces?
12.1 Force
12.4 Universal Forces
What are the four fundamental forces

Electromagnetic Forces
 Associated with charged particles
 Electric Force – between two charged particles
 Negative and positive
 Opposites attract, like repels
 Magnetic Force – between other
magnets and certain metals
12.1 Force
12.4 Universal Forces
What are the four fundamental forces

Strong Nuclear Force
 Act to hold the nucleus together
 Overcomes repulsion of positive protons with each
other
 The strongest force over small
(tiny, tiny) distances
12.1 Force
12.4 Universal Forces
What are the four fundamental forces

Weak Nuclear Force
 Involved in certain types of radioactive processes
 Active only over distances even smaller than the
strong nuclear force
12.1 Force
12.4 Universal Forces
What are the four fundamental forces

Gravitational Force
 Between any two objects with mass
 Depends on the mass and the distance between
the objects
 Very weak force
 Acts over
very long
distances