Transcript Newton`s Laws of Motion

Newton’s Laws of Motion
Gravity and Motion
Gravity

A force of attraction between objects that
is due to their masses.
Because gravity is
less on the moon
than on Earth,
walking on the
moon’s surface was
a very bouncy
experience for the
Apollo astronauts.
July 20, 1969
All Matter Is Affected by Gravity
All objects experience an attraction toward
all other objects.
 Because of gravity you are being pulled
toward the Earth, your pencil, and every
other object around you are also being
pulled. Do you know why?

Earth’s Gravitational Force Is Large
“It’s Truly Incomparable”, on Earth
Compared with “all” the objects around you,
Earth has a enormous mass.
The Law of Universal Gravitation
Why do objects fall toward Earth?
 What keeps the planets in motion in the
sky?

Newton Makes the
Connection
The Law of Universal Gravitation states that all
objects in the universe attract each other
through gravitational force. The size of the force
depends on the masses of the object and the
distance between them.
For Example…

Gravitational force increases as
mass increases.
Imagine an Elephant and a Cat
 Imagine the Earth and the Moon


Gravitational force decreases as distance
increases.
Gravity between you and the Earth
 Gravity between you and the Moon

Weight and Mass are Different


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Weight is a measure of the gravitational force
exerted on an object.
Weight, a force, is measured with a spring scale.
Mass is the amount of matter “Stuff” in an object,
and its value does not change.


Mass is measured with a balance.
If an object is moved to a place “Geographically
Speaking” with a greater gravitational force (Jupiter)
its weight will increase, but its mass will remain the
same.
Newton’s First Law

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.
INERTIA

Objects at “Rest”… Can move
Objects in Motion… Meaning ?
This law is also sometimes called the
law of inertia. Why?


Inertia is the tendency of all object to resist any
change in motion.

Mass is a measure of inertia.


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Little mass-little inertia
Big mass-big inertia
Inertia – How is this related to seat belts in
moving vehicles?
Newton’s Second Law
The acceleration of an object depends on
the mass of the object and the amount of
force applied.
 Acceleration describes the motion of an
object when an unbalanced force is acting
on it.


Acceleration depends on mass
 More

mass – More force
Acceleration depends on the force applied or
needed to move the mass
If the force applied is the same, the acceleration of
the empty cart is greater than the acceleration of
the full cart.
Acceleration – You need more force to move
more mass.
Newton’s Second Law and
Acceleration are due to Gravity
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.

All forces act in pairs. What does this
mean?

Think about a balloon or rocket.
“Momentum Anyone?”

Momentum is a property of a moving
object that depends on the object’s
mass and velocity.
The more momentum an object has – the
harder it is to stop it or change it’s
direction.
 Think about a bowling ball and ping pong
ball


Momentum is Conserved. Just how is this
done?
Momentum is Conserved
The momentum before a collision is equal to
the momentum after the collision.
For Review…

How does the mass of an object relate to
the gravitational force the object exerts on
other objects?

How does the distance between objects
affect the gravity between them?

Comparing Concepts: Explain why your
weight would change if you orbited Earth
in the space shuttle but your mass would
not?

How is inertia related to Newton’s First
Law of Motion?

Name two ways to increase the
acceleration of an object.

What are the two things associated with
Newton’s Third Law?

Name three action and reaction force pairs
involved in doing your homework. Name
what object is exerting and what object is
receiving the forces.

Which has more momentum, a mouse
running at 1 m/s north or an elephant
walking at 3 m/s east? Explain your
answer.