Transcript Gravity Newton`s Laws of Motion

Gravity
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 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.
http://phet.colorado.edu/en/simulation/gravity-force-lab
The Law of Universal Gravitation
Discovered by Newton in
the late 1600’s while he
watched an apple fall from
a tree
 He said that the force that
pulled the apple to the
ground was the same force
that keeps the moon and
earth in it’s orbit

The Law of Universal Gravitation

Universal Gravitation:
Two bodies attract each
other with equal and
opposite forces
,

The magnitude of this
force is proportional to
the product of the two
masses and is also
proportional to the
inverse square of the two
bodies.
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.
Misconceptions


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Astronauts are not
experiencing weightlessness.
They are in free fall along
with all the other objects
around them. Since they are
all “falling” at the same rate
Without air resistance, all
objects will drop at equal
rates
Skydivers are not in “free fall”
because air resistance is also
acting on them.
Free Fall
 Occurs
when the only force acting on a
object is gravity
 All objects in free fall accelerate at the s
rate
Projectile Motion
Has 2 components
 Consists of vertical
and horizontal
velocities
 Horizontal = launch
 Vertical = gravity
 Causes a curved path
 This is why you should
always aim a target

Video: Are Astronauts Weightless
Video: Zero G Jet
Video: Zero G Jet 2
Acceleration are due to Gravity
Acceleration due to gravity = g = 9.8 m/s2
Video: Misconceptions about
falling objects
Video: No Air Resistance
Terminal Velocity
Both gravity and air resistance act on
falling objects
 Objects accelerate as they fall
 If/when air resistance equals the
gravitational force (balances the weight)
no more acceleration occurs
 When acceleration stops, a maximum
velocity is reached. Its called terminal
velocity.

Video: Terminal Velocity
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?
Other Videos:
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