Newton's Laws of Gravitation

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Newton's Universal Law of Gravitation

A teacher can even exert a force of

gravitation on their students!

Click here to see a video on the Law of

Gravitation

Any two objects with mass will exert a force of attraction
to each other even over vast distances. This force acts on

both objects, pulling them towards each other.

Multiple Select

3 What factors affect the force of gravity between two
objects? (Choose all that apply.

• mass of the object

• weight of the objects

• distance between the objects

• force of the objects

Multiple Choice

What happens to the force of gravity between two
objects as they move apart?

• Increases due to distance

• Decreases due to distance

• Nothing because the masses dont change

• impossible to tell without knowing what the objects
  are

Multiple Choice

When talking about the gravity between you and Earth,
Earth has a larger force acting on it than you do.

• True

• False

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Mathematical Relationships in Physics

Before we discuss the law of gravitation in great detail, it is important to understand basic mathematical relationships used in science. We can

"read" equations to determine how the variables in the equations affect each othe

Mathematical relationships tend to be classified into two main categories.

Directly Proportional

&

Inversely Proportional

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Directly Proportional

What is meant by the term "directly proportional"?

Example:

A child is paid $1.00 per paper delivered on his/her newspaper

route. If they deliver more papers, they earn more money.

This works in reverse as well, if the child's bicycle chain breaks and they

deliver less papers, then he/she makes less money.

In an equation, as one amount increases, another amount increases at the same rate.

Multiple Choice

A college student increases her time studying. Her
test grades also increase. What is the relationship
between time studying and earned grades?

• Inversely Proportional

• Directly Proportional

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Inversely Proportional

In an equation, as one amount increases, another
amount decreases at the same rate.

Example:

As the paperboy increases his/her speed of delivery, the time it takes to complete his/her route decreases!

And as the paperboy decreases his/her speed of delivery, the time it takes to complete his/her route increases!

​the time it takes to complete
his/her route increases!

Multiple Choice

A person increases their distance away from a light
bulb, the observed brightness decreases. What is
the mathematical relationship observed during this
event?

• Inversely Proportional

• Directly Proportional

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8 As the voltage in a circuit is increased, the amount of
electrical current is also increased. What is the
mathematical relationship observed during this event?

A
Inversely Proportional

B
Directly Proportional

Multiple Choice

A college student increases her time studying. Her
test grades also increase. What is the relationship
between time studying and earned grades?

• Inversely Proportional

• Directly Proportional

Multiple Choice

As the resistance in a circuit is increased, the amount
of electrical current is decreased. What is the
mathematical relationship observed during this event?

• Inversely Proportional

• Directly Proportional

Multiple Choice

As the resistance in a circuit is increased, the amount
of electrical current is decreased. What is the
mathematical relationship observed during this event?

• Inversely Proportional

• Directly Proportional

Multiple Choice

We know that the force of gravity between two objects
increases as the masses get larger. This relationship is
___________ proportional.

• Inversely

• Directly

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Compare the force of gravity acting on you

(your weight) on Earth compared to the moon:

Which is larger? WHY?

Comparing Forces of Gravity

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A

B

C

What happens to the force of gravity on an object as we
move farther away from a massive object like Earth?

With your group, compare the force of gravity (weight of boy) at

points A, B, & C and be ready to share.

Comparing Forces of Gravity

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The force of gravity exerted by an object decreases as it

moves away from an object like Earth.

As the boy moves away from Earth, his weight will decrease.

Distance and Forces of Gravity

Multiple Choice

As the same boy from the last slide moves farther from
Earth, will his mass change?

• yes

• no

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Why can't we feel the forces of Gravitation

acting between two people?

Small Masses = Small Force of Gravitation

Even though there is always a gravitational force acting between

masses, it is only noticeable when the objects' masses

are relatively large.

If we were to compare our mass to that of a planet, a person's mass is so small that the gravitational force they produce is almost unmeasurable.

Multiple Choice

The force of gravity _________ as the
object's mass increases.

• Increases

• Remains constant

• Decreases

Multiple Choice

The force of gravity _________ as the
distance between two objects increases.

• Increases

• Remains constant

• Decreases

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The force of gravity does not decrease at a constant rate

as an object moves away from a planet.

The Force of Gravity actually decreases

exponentially as distance increases!

Distance and Forces of Gravity

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If we graph the force of
gravity (Newtons) vs.
distance of separation
(m) of an object as it
moves away from a
planet, this is what we
get:

Distance and Forces of Gravity

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The decrease in the force of gravity does not decrease at a
constant rate. If it did the graph would look like this:

Note: This graph is not the real
pattern we observe in nature.

Distance and Forces of Gravity

Multiple Choice

Force is ___________ proportional to distance.

• Directly

• Indirectly

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The true pattern observed by
scientists showed that the
force of gravity is inversely
proportional to distance of
separation squared!

Distance and Forces of Gravity

F = 1
d2

NOTE: This is almost the same
as regular inversely proportional,

but the force decreases much
more as distance increases

because it is squared.

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Putting it all together

Putting all these ideas together, fill in the blanks below with the
correct mathematical relationships.

d

The Gravitational Force between 2 masses is

__________________ to the product of the masses and

________________ to the distance of the separation squared

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We can represent the
gravitational field around
a mass with lines of force.

The lines point inward and
then spread apart as we
move away from Earth.

Why? Come up with an
idea with your table.

Gravitational Field Lines

Multiple Choice

The force of gravity decreases at a constant rate as
we move away from a planet like Jupiter.

• True

• False

Multiple Choice

As we move away from the Sun, the force of gravity
gets weaker by an inverse of the:

• distance cubed

• 
  distance

• distance squared