Transcript Gravity - My CCSD

Planetary Motion 4/29/15
19-1b pgs. 515-518
IN: What causes
night and day?

Rotation

As the Earth rotates, only one-half of the
Earth faces the sun at any given time.

Rotation – the spinning
motion of a body on its axis.
•On Earth rotation causes night
and day.
Day Night Cycle
Night and Day

http://www.cs.sbcc.net/~physics/fla
sh/LengthofDay.swf

Revolution – the elliptical
motion of a body as it orbits
another body in space.

The period of revolution for
the Earth to revolve around
the sun is 365.25 days.
Planetary Motion


Most objects in space move
according to strict physical laws.
The way in which the Earth moves,
for example, causes seasons and
even day and night.
Kepler’s Laws of Motion
1st Law –Planets orbit the sun in a
closed curve called an ellipse.
2nd Law –Planets seem to move
faster when they are close to
the sun and slower when they
are farther away.
3rd Law –Planets close to the sun
orbit faster than planets far
away from the sun.
Planets
Newton’s Law of Universal Gravity
Gravity – the attractive force
of one object on another
object.
The strength of the gravitational force
between two objects is dependant
on two factors:
1. mass of the objects
• the more massive the object the
greater the gravitational force
2. the distance between the two
objects
• the closer the objects are together,
the greater the gravitational force
between them
The two biggest gravitational forces
that we notice are:
1. The sun (1.98892 x 1030 kg) is the
most massive object in our solar
system and exerts a huge
gravitational force. This is why all the
planets stay in orbit around the sun.
2. The Earth (5.9742 x 1024 kg) is so
massive that its gravitational force
keeps us from falling off the planet.
When astronauts
go into space,
they “float”
because they
are far enough
away from the
center of the
earth that the
gravitational
force isn’t strong
enough to hold
them down.

OUT: Will a planet
or comet be moving
faster in its orbit
when it is farther
from or closer to
the sun? Explain.