Transcript Gravity Newton`s Laws of Motion

Gravity
Newton’s Laws of Motion
Chapter 5: Section 4
Chapter 6: Section 2
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.
All Matter Is Affected by Gravity
All objects experience an attraction toward
all other objects.
 Because of gravity you are being pulled
toward this book, your pencil, and every
other object around you. Do you know
why?

Earth’s Gravitational Force Is Large
“It’s Truly Incomparable”
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
 Or imagine the Earth and the Moon


Gravitational force decreases as distance
increases.
Gravity between you and the Earth
 Gravity between you and the Sun

Weight and Mass are Different



Weight is a measure of the gravitational force
exerted on an object.
Do you know what that means?
Mass is the amount of matter “Stuff” in an object,
and its value does not change.

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 Laws of Motion
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.

Objects at “Rest”… Let’s share some of
the many examples illustratively “Smile”

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.
Newton’s Second Law

The acceleration of an object depends on
the mass of the object and the amount of
force applied.
Acceleration depends on mass
 Acceleration depends on force

If the force applied is the same, the acceleration of
the empty cart is greater than the acceleration of
the full cart.
Acceleration will increase when a larger
force is exerted.
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?
Action and Reaction Forces
“Momentum Anyone?”

Momentum is a property of a moving
object that depends on the object’s mass
and velocity.

Momentum is Conserved. Just how is this
done?
The momentum before a collision is equal to
the momentum after the collision.

Conservation of Momentum and Newton’s
Third Law
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?

When you stand while riding a bus, why do you
tend to fall backward when the bus starts
moving?

See page 724 to check your answer

How is inertia related to Newton’s First Law of
Motion?

Name two ways to increase the acceleration of
an object.

Making predictions: If the acceleration due to
gravity were somehow doubled to 19.6 m/s/s,
what would happen to your weight?

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.

Applying Concepts: When a truck pulls a trailer,
the trailer and truck accelerate forward even
though the action and reaction forces are the
same size but in opposite directions. Why don’t
these forces balance each other out?