Transcript
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?
HOMEWORK
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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
HOMEWORK
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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
HOMEWORK
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