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https://www.youtube.com/watch?v=ttZCKAMpcAo
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Gravity: A force of attraction
Make things move….faster, slower and change
direction…also gravity makes them change shape…
READING:
Gravity: A force of Attraction (574 – 579)
Answer the 10 questions from page 579 in
your notebook
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Sir Isaac
Newton
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Why do objects fall toward the Earth, and what keeps the planets
moving in the sky?
https://www.youtube.com/watch
?v=jwPc0kK9VHU
The law of universal gravitation describes the relationships between gravitational
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force, mass and distance.
The Law of Universal Gravitation
All objects in the universe attract each other through
gravitational force
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PART 1
PART 2
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Distance,
Mass, Fg
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•
•
•
•
•
Remember
All matter has mass
All matter is affected by gravity
All objects experience an attraction toward all other objects
Because of gravity you are being pulled right now!
Why don’t you notice objects moving toward each other?. Mass is too
small.
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Weightless?
(NASA pictures)
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WEIGHT IS A MEASURE OF GRAVITATIONAL FORCE
GRAVITY is a force of attraction between objects due to their
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masses.
So when gravity pulls something towards the Earth, we can
call this force WEIGHT
(W)
W = mg
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So when gravity pulls something towards the Earth, we can
call this force WEIGHT
N=
(W)
W = mg
Kg. m
S2
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What is “g”?
'g' is the gravitational field
strength
 the force with which gravity
pulls each kilogram of mass.
W
=
mg
w = mg
W
=
(100
kg)
(9.83
N/Kg)
= mg
w = (100wkg)
(9.83 N/Kg)
W = 100 x 9.83 N
W = 983 N
The force of gravity you experience due to the Earth
(w) is proportional to your own mass (m).
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apparently weightless
(pictures or animation only –not a demonstration)
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On the Moon – Apollo 15
A heavy geological hammer and a
falcon feather were dropped from
the same height.
They hit the lunar surface at the
same time.
astronaut David Scott
•
NASA pictures
http://www.youtube.com/watch?v=MJyUDpm9Kvk
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Very heavy bootsWhy?
Answers?
• No gravity on the Moon
• Weightless on the Moon
• To stop them floating away
• They weigh very much less
than on Earth
• To stop huge bounces
• The Moon’s gravity is very
much less than the Earth’s
gravity
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GRAVITY
No Gravity
• Things fall
• Things have weight
• Things stay in place
Would an apple
fall?
Would things stay
on earth?
What would
happen?
What?
Why?
How?
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“If Wile E. Coyote and a boulder fall off a cliff at the
same time, which do you think will hit the ground
first?”
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two objects
dropped at the
same time
GALILEO
GALILEI
https://www.youtube.com/watch?v=NMM8vx9vDiE
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https://www.youtube.com/watch?v=_mCC-68LyZM
GRAVITY AND
ACCELERATION
Objects fall to the ground at the same rate because
the acceleration due to gravity is the same for all objects.
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ACCELERATION DUE TO
GRAVITY
It means that every second that an object
falls, the object’s downward velocity
increases by 9,8 m/s²
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All objects
accelerate
toward
Earth at a
rate of 9,8
m/s²
Velocity of a falling object:
ΔV=gxt
ΔV = final velocity – starting velocity (m/s)
g = acceleration due to gravity (9,8 m/s²)
t = time the object takes to fall in seconds
SOLVE MATH FOCUS EXERCISES (PAGE 591 IN YOUR
COPIES)
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Net Force = 0 N
A stops
X
X
Only gravity is pulling the object down
Constant velocity
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AN ELEPHANT AND A
FEATHER
Suppose that an elephant and
a feather are dropped off a
very tall building from the
same height at the same
time.
Which object - the elephant or
the feather - will hit the
ground first?
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As air pressure decreases, the potential for air
resistance also decresases.
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WHAT’S ORBITING?  AN
OBJECT IS ORBITING WHEN IT IS
TRAVELING AROUND ANOTHER
OBJECT INTHE SPACE
Orbiting and free falling
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Launching a satellite
• The cannon
ball must move
very quickly to
orbit the
earth.
The Moon orbits
the Earth
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THIS MOTION IS A CURVED PATH WHEN IT IS
THROWN OR PROPELLED NEAR THE SURFACE
OF THE EARTH
MOTION PARALLEL TO
THE GROUND
MOTION DOWNWARD
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HOMEWORK
READING:
Gravity and Motion(590 – 597)
Answer the 10 questions from page 597 in
your notebook
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