Transcript 4.2 Gravity - Trimble County Schools

4.2 Gravity
Objectives
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Describe the gravitational force.
Express the dependence of gravitational field on mass and
distance, using proportions.
Distinguish between mass and weight.
Gravity
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The force of attraction that exists between
all matter in the universe.
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Key word is matter
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Matter is the stuff you are and everything
else is made of
It takes a lot of mass for the gravity to be
noticeable.
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Like planetary mass
Law of Gravity
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The force of attraction between any two
objects depends on their masses and the
distances between them.
The bigger the object, the more gravity it has
 The closer an object is to something the
stronger the pull.
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4 Basic Forces
1.
2.
Gravity
Electromagnetic Force
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3.
4.
Causes electricity and magnetism
Also causes chemical interactions between
atoms and molecules
Strong Nuclear Force
Weak Nuclear Force
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Along with Strong Nuclear Force – only act on
particles in the nuclei of atoms
Law of Universal Gravitation
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Formulated from Newton’s data on motion of
planets in 1687
Law of Universal Gravitation
• G is a constant called the universal gravitational
constant
• d is the distance between the two masses, m1 and
m2.
• Enables us to calculate the force of gravity
between any two objects if their masses and the
distance between them is known.
Range of Gravity
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Gravity’s force depends on how close the
object is to something.
As an object gets further away, the force of
gravity on that object decreases
Inverse square law
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As the distance increases the gravity decreases
exponentially
Universal Gravitation
Because it relates to all matter, on earth as
well as the planets and stars
 Earth’s motion is affected by the
gravitational pull of other planets
 1846 – astronomers used
Law of Universal Gravitation
to discover Neptune due to
its pull on Uranus
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Gravitational Acceleration
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When all forces except gravity are ignored,
falling object is in free fall
 All objects fall at same acceleration in free
fall = 9.8 m/s2
By Newton’s second law of motion, the force
of Earth’s gravity on a falling object is the
object’s mass times the acceleration of
gravity.
 F=mg
Weight
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Gravitational force exerted on an object
g = Gravitational acceleration constant 9.8
m/s2
Weight, Mass, and Gravity
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Mass
How much matter you
are made of
Does not change
depending location
It is the same if you are
on earth or in space or
on the moon
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Weight
The relationship
between mass and
gravity
Changes depending on
location
Is different on earth
and the moon and
space
Weight
•The table shows how various weights
on Earth would be different on the
Moon and some of the planets.
In-Class Assignment