Transcript Newton's Laws of Motion

Background
Sir Isaac Newton (1643-1727) an English
scientist and mathematician famous for his
discovery of the law of gravity also discovered
the three laws of motion. He published them
in his book Philosophiae Naturalis Principia
Mathematica (mathematic principles of
natural philosophy) in 1687. Today these
laws are known as Newton’s Laws of Motion
and describe the motion of all objects on the
scale we experience in our everyday lives.
“If I have ever made any
valuable discoveries, it has
been owing more to patient
attention, than to any other
talent.”
-Sir Isaac Newton
Newton’s First Law of Motion

An object at rest remains at rest, and an
object in motion remains in motion at
constant speed and in a straight line
unless acted on by an unbalanced force.

A golf ball will remain at rest on a tee until it is
acted upon by unbalanced forces of a moving
club.
Breakin’ it Down into parts…
Part 1: Objects at rest.
 An object that is not moving is said to be at
rest.
 Newton’s 1st Law says that objects will stay at
rest unless acted by an unbalanced force.
 Objects will not start to move until a push or
pull is exerted on them.

Part 2: Objects in Motion
 Objects will continue to move with the same
velocity unless an unbalanced force acts on
them.


Think about bumper cars! Your bumper cars stops
when it hits another car. But, you continue to move
forward until the force from your seat belt stops
you.
Think about this….

When you ride a bus, why do you fall forward
when the bus stops moving?

When the bus is moving, both you and the bus
are in motion. When the bus stops moving, no
unbalanced force acts on your body, so your
body continues to move forward.
Newton’s Second Law of Motion

The acceleration of an object depends
of the mass of the object and the
amount of force applied.
Part 1: Acceleration Depends on Mass
 The acceleration of an object decreases as its
mass increases, and that its acceleration
increases as its mass decreases.



Suppose you are pushing an empty cart.
You have to exert only a small force on the cart to
accelerate it. But, the same amount of force will not
accelerate the full cart as much as the empty cart.
Part 2: Acceleration Depends on Force
 An object’s acceleration increases as the force
on the object increases, and an object’s
acceleration decreases as the force on the
object decreases.
 The acceleration of an object is in the same
direction as the force applied.


Suppose you give the cart a hard push, the cart will start
moving faster than if you gave it only a soft push.
The Mathematics….
M = 0.102 kg
F=1N
 What
M = 1.02
F = 10 N
is the acceleration of the apple
and the watermelon?
M = 0.102 kg
M = 1.02
F=1N
F = 10 N


a=F
m
a = 1 kgm/s2 = 9.8 m/s2
0.102 kg


* 1 N = 1 kgm/s2
a=F
m
a = 10 kgm/s2 = 9.8 m/s2
1.02 kg
What is the acceleration…

Of a 3 kg mass if a force of 14.4 N is
used to move the mass?
a=F
m
 a = 14.4 kgm/s2 = 4.8 m/s2
3 kg

Newton’s Third Law of Motion

Whenever one object exerts a force on a
second object, the second object exerts
an equal and opposite force on the first.
All forces act in pairs!

If a force is exerted, another force
occurs that is equal in size and opposite
in direction.

The way the force pairs interact affects
the motion of objects.
Action and Reaction…

When a force is exerted, there is always
a reaction force.
 For
every action, there is an equal
and opposite reaction.
Other examples of Newton’s Third
Law

The baseball forces
the bat back (an
action); the bat forces
the ball forward (the
reaction).

Consider the motion of a car on the way to
school. A car is equipped with wheels which
spin backwards. As the wheels spin
backwards, they grip the road and push the
road backwards.