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Newton’s Laws
Solar System
Galileo & Copernicus
explained:
The Sun was in the
center of the solar
sytem

Kepler explained:
• Planets have elliptical
orbits around the Sun
• Planets orbit at different
speeds.
• Planets cover equal area
in equal time.
• The farther the distance
from the Sun, the greater
the orbital period.
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Isaac Newton (1642 – 1727)



One of the most brilliant
theoreticians to ever live.
WHY
Explained
the
planets move as they do.
He formulated three laws of
motion and the law of universal
gravitation.
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Terms to describe motion


FORCE:
A push or pull
that changes the
motion of an
object


VELOCITY:
Describes how
fast (speed) an
object moves in
a direction
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Forces and Motion
Station #1
In a long, unobstructed hallway, on the smooth floor surface, exert a force (push) on a marble to change its velocity. Observe and describe the
velocity, direction and distance of the marble.
Station #2
Exert a small force (push) on the ball to give it velocity across the table top. Observe /compare its path on the table and when it rolls off the table.
Station #3
Using a full paper plate, place the marble inside the inner rim and roll the marble to change its velocity so it has circular
motion. What force is being exerted that is keeping it in a circular orbit?
Using the cut-out plate, place the marble inside the inner rim and roll the marble. Observe it motion.
Station #4
Hold the end of the string. Slowly accelerate the “moon” so it travels in a circular orbit. Let of the string. Describe the path of the ball.
Station #5
Hold the spool and slowly twirl the ‘satellite’ around in an orbit. Change the speed of the ‘satellite’ and observe.
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Newton’s 1st Law of Planetary Motion
Unit 2
PHENOMENON:
What did you observe?
What evidence do you have?
OBJECTS:
Define the
system.
What objects are
interacting?
MODEL:
Describe the motion or the model that explains your
observations
Station #1
Station #2
Station #3
Station #4
Station #5
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Newton’s 1st Law of Inertia:
Objects in uniform straight line motion continue in
straight line motion unless an outside force is
applied to change their motion
Once in orbit, a planet
will CONTINUE its orbital
motion at constant
velocity until an outside
force (asteroid, another planet?)
acts on it to change its
orbit.
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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
object.
Forces are interacting in PAIRS – one object on another
“To every action there is an equal and opposite re-action.”
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Law of Universal
Gravitation
Mass attracts mass
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If the Earth’s gravity force is attracting the moon,
Then Why doesn’t the moon get pulled into Earth?
The moon has
VELOCITY!
It’s moving with a
constant speed in a
direction – straight.
As long as the FORCE of gravity toward Earth is EQUAL to
the forward motion of velocity of the moon it will ORBIT
Newton’s Second Law:
what causes objects to move
Newton understood that to change the
motion of an object (ACCELERATE it) a
FORCE must be applied to it (it’s MASS)
Acceleration = Force
Mass
or
F=mxa
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Newton’s Second Law
Example problem:
What FORCE is necessary to accelerate a 1250 kg
asteroid at a rate of 40 m/s2?
Formula
F=mxa
Plug-in numbers
F = 1250 kg x 40 m/s2
Solve and Units
50,000 N
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