SECTION 7.2Using the Law of Gravitation

USING THE LAW OF UNIVERSAL GRAVITATION

What is Newton’s Law of Universal Gravitation and

how do I apply it?

SATELLITES

GPS

Cable

Weather

What is the shape of their orbit?

What force comes to mind?

HOW DO THEY STAY UP?

Discovered before we even had satellites by

Newton

Giant Cannon

ORBITAL PERIOD

VELOCITY OF A SATELLITE

EXAMPLE

A satellite orbits Earth

225 km above its

surface. What is the

orbital speed and

period?

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MORE NLUG

How do I describe weightlessness?

How do I describe gravitational fields?

MINI-LAB

FINDING ACCELERATION DUE TO GRAVITY

GRAVITATIONAL FIELD

Is gravity a contact force?

Michael Faraday developed the theory of field

forces when applied to magnetism

Also applies to gravity

GRAVITATIONAL FIELD

EARTH’S GRAVITY

Based on the

equation, what

happens to g as we

move away from the

Earth?

EXAMPLE

Space shuttle orbits 4000 km above the Earth.

What is g at this height?

WEIGHTLESSNESS

So if there is gravity, why do astronauts float?

WEIGHTLESSNESS

We experience weight because of the normal force

pushing back on us

Earth is providing the gravity

In space, everything is experiencing the same

acceleration due to gravity

So, no normal force

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TWO KINDS OF MASS

How can I describe and measure the two different

types of mass?

INERTIAL MASS

Using Newton’s

second:

m = F/a

Resistance to

movement

GRAVITATIONAL MASS

ALBERT EINSTEIN

Said that inertial and gravitational mass are the

same

Principle of equivalence

So far has held true

Basis in the theory of gravity

EINSTEIN’S THEORY OF GRAVITY

Gravity is not a force, but

an effect of space itself

Mass changes the space

around it

Mass causes space to be

curved, and other bodies

are accelerated because

of the way they follow this

curved space.

DEFLECTION OF LIGHT

Einstein’s theory

predicts the deflection

or bending of light by

massive objects

Light follows the

curvature of space

around the massive

object and is deflected.

BLACK HOLE

If an object is large enough, light cannot escape

Black Hole

Have been identified by their effect on nearby stars

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