Transcript The Motion of the Universe

The Motion of the Universe
What Keeps Celestial Bodies in
Orbit?
 The First Person to attempt to answer
this question was
Isaac Newton
•Formulated the Law of Universal Gravitation
Every object in the universe attracts every other object
•Force of gravity depends on two factors
Mass of the object
If mass increases, gravity increases
Distance between objects
If distance increases, gravitational attraction
decreases
Objects with greater mass attract those with less mass
So why doesn’t Earth fall into the Sun?
 Remember Newton’s First Law of
Motion: Inertia keeps it in motion!
 Inertia is the tendency of an object to stay at
rest or in motion. (affected only by mass…
^mass = ^ inertia)
 First Law of Motion States:
 An object at rest will stay at rest or an object in
motion will stay in motion unless acted on by a
unbalanced force
This holds true for all object orbiting other
objects in the universe!
Orbit of the Earth is determined by
inertia and gravity
 An objects orbit is the location where
the two forces are in balance (net
force = 0)
If two objects are in the same
orbit but one has less mass, what
will have to be different about the
two objects
Newton vs. Einstein
 Newton thought that gravity was an
instant force and did not take time to
travel.
 Einstein felt gravity moved like light –
at a particular speed and propagated
out from a source
Einstein’s Theory of General
Relativity
 Objects warp space
 Objects orbit
because they are
pushed or pulled
into indentations
that are created by
other larger objects
Kepler’s First Law: Orbits of
Celestial bodies
 Kepler's first law sometimes referred
to as the law of
ellipses - explains
that planets are
orbiting the sun in a
path described as an
ellipse
Kepler’s Second Law
 The speed at which any planet
moves through space is
constantly changing.
 A planet moves fastest when it is
closest to the Sun and slowest
when it is furthest from the Sun.
 But if a line were drawn from the
center of the planet to the center
of the sun, that line would create
a triangle of equal area.

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