Transcript Inertia, Gravity and Planet Orbits

What is rotation?
• Spinning on an
imaginary axis
• Period of rotation is
the time it takes for
a planet to make 1
spin on its axis
=length of a planet
day
What is revolution?
• A planet’s movement
around the sun is a
path called an orbit
• Period of revolution is
the time it takes for a
planet to orbit around
the sun = length of a
planets year
What is the shape of the
planets’ orbits around
the Sun?
Ellipse –
Oval in shape. It
has 2 fixed
points called foci
What is meant by
eccentricity?
• The degree of “ovalness” of an ellipse
• Ranges from zero to one.
– 0 is a perfect circle, the closer to 1 the more
oval
– 1 is a straight line
What is the formula
for eccentricity?
• Eccentricity= distance between foci (d)
Length of major axis (L)
Example
Eccentricity = __1.1 cm__
4.7 cm
= 0.234
Compare the
eccentricity of
this orbit to that
of Saturn’s orbit.
Are the planets always the same
distance from the sun?
No, because of the elliptical shape of the
planet orbits, they vary in distance from
the sun during revolution.
What is perihelion?
• When Earth is closest to the sun.
• Since the Earth is closest to the sun it
will have the largest apparent diameter
during the year (look bigger)
• Greatest force of gravity between Earth
and Sun
When is the Earth in
Perihelion?
During winter - January 3rd
What is aphelion?
• When Earth is farthest from the sun
• Since the Earth is farthest from the sun it
will have the smallest apparent diameter
during the year (look smaller)
• Least gravitational force between Earth &
Sun
When is the Earth in
Aphelion?
During summer – July 4th
What two forces balance a
planet’s revolution?
The two forces that balance out the
planet’s revolution would be:
Gravity & Inertia
What is inertia?
An object in motion, stays in motion and
an object at rest, stays at rest unless acted
on by an outside force
What is gravity?
An attractive force that exists between any
2 objects in the universe.
What effect does mass
have on gravity?
The greater the mass, the greater the
force of gravity
What effect does distance
have on gravity?
The closer the object are to each other
the greater the force of an object.
What is Kepler’s law
of equal areas?
A planet sweeps out equal areas
in equal amounts of time
A must = B
When does a planet have its
fastest orbital velocity?
When it is closest to the sun (perihelionwinter), because the gravitational pull is
largest.
At which location does
this occur?
When does a planet have its
slowest orbital velocity?
When its farthest from the sun (aphelionsummer), because the gravitational pull is
smallest.
At which location does
this occur?
1) At which letter, does the apparent diameter of the sun
appear the largest?
2) At which letter, does the apparent diameter of the sun
appear the smallest?
3) What season occurs at letter A?
4) What season occurs at letter C?
5) What season occurs at letter B?
6) What season occurs at letter D?
7) What happens to the orbital velocity as you move from
point A to C?
8) What happens to the orbital velocity as you move from
point C to A?
9) What happens to the orbital velocity as you complete
one revolution starting from point C?
10)What happens to the orbital velocity as you complete
one revolution starting from point A?