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Mars moon Phobos, as seen by ESA's Mars Express. Phobos is about 25 kilometers in length and does not have enough gravity to compress it into a ball. It orbits so close to Mars that sometime in the next 20 million years, tidal forces will break up Phobos into a ring whose pieces will slowly spiral down and crash onto the red planet. The Russian mission Phobos-Grunt is scheduled to launch and land on Phobos next year.
Out-of-class Activity:
Every clear Wednesday evening
for the rest of the semester.
Check website for details.
Kirkwood Observatory Open House
A100 Movie Special
Tuesday, March 23
Swain West 119
7:00 pm (153 minutes)
Winner of several awards
20 activity points!
Homework #6 is
due Wednesday, March 24, 2:30 pm
Homework #7 will be posted shortly. It will be due next Monday
Exam #2
Wednesday, March 31
Review session will be held next Monday, time and location to be announced
Newton’s Three Laws of Motion
Newton’s Law of Gravity
The Acceleration of Gravity (a force)
As objects fall, they accelerate (a = g = Fgrav/m).
We use the special symbol g to represent the acceleration due to the force of gravity.
At sea level on the Earth, g = 9.8 m/s each second,
or g = 9.8 m/s2.
The higher you drop the ball, the greater its velocity will be at impact (force will be acting on it longer).
Weight is the force of gravity acting upon an
object :
W = Fg = mg
Galileo demonstrated that g is the same for all objects, regardless of their mass!
Is Mass the Same Thing as Weight?● mass – the amount of matter in an object● weight – a measurement of the force due to
gravity acting upon an object
When in free-fall, you still have weight!
“weightless” is a misnomer
W = mg (weight) F = ma
● Objects do have weight in space
● Free-fall often confused with weightlessness
Now, some questions…
Tidal Forces Because the gravitational force decreases with (distance)2, the attractive
force experienced by one object (e.g., the Earth) due to the gravitational field of a second object (e.g., the Moon) varies with position (closest parts attracted most strongly).
● Now look at what happens when we measure the forces
relative to the center of the Earth.
Tidal Friction
Tidal Friction
● This fight between Moon’s pull & Earth’s rotation causes friction.
● Earth’s rotation slows down (1 sec every 50,000 yrs.)
● Conservation of angular momentum causes the Moon to move farther away from Earth.
Synchronous Rotation● …is when the rotation period of a moon, planet, or star
equals its orbital period about another object.
● Tidal friction on the Moon (caused by Earth) has slowed its rotation down to a period of one month.
● The Moon now rotates synchronously.– We always see the same side of the Moon.
● Tidal friction on the Moon has ceased since its tidal bulges are always aligned with Earth.
● Most of the large moons in the solar system are in synchronous rotation.
Now we are ready to examine the solar system!!
We want to understand how the solar system was formed and how it got to be in the state that it is today.
Look for patterns and physical characteristics of the solar system.
What does any theory of the formation and evolution of the solar System have to account for?
The Sun:
A fairly typical star
Predominately H and He
Most of the mass in the solar system.
Rotates in same sense that planets
orbit.
Need to understanding the similarities and differences between the planets, moons, asteroids, & comets
Nine planetseig
ht
People of earth.
Help!!!!
Planetary orbits:
1) Prograde
2) approximately coplanar
3) approximately circular
Rotation:
1) Mostly Prograde
2) Includes sun
3) Includes large moons
Terrestrial Jovian
Two “flavors” of planets
Size – “smaller” Location – closer to Sun Composition – rocky/metallic Temperature – hotter Rings – none Rotation rate – slow Surface – solid Atmosphere – “minimal”
Terrestrial Planets
Mer
cury
Mar
s
Ven
us
Ear
th
Mercury
No moons
Venus
No moons
Earth
One moonMars
Two moons
Jovian Planets
Size – “larger” Location – farther from Sun Composition – gaseous (mostly H,He) Temperature – cold Rings – ubiquitous Rotation rate – fast Surface – not solid Atmosphere – substantial
Jupi
ter
Nep
tune
Sat
urn
Ura
nus
Jupiter
>61 moonsUranus
> 27 moons
Neptune
> 13 moons
Saturn
> 31 moons
Surface features of solid objects in solar system
Craters are ubiquitous
There are lots of smaller objects in the Solar System,
some are rocky and some are icy
small
Rocky
Odd-shapes
nearly circular orbits
orbit planes are near Ecliptic Plane
orbits in inner part of solar system
Asteroids
The “asteroid belt”
Asteroids
Mars’ moons and the asteroid Gaspra
Deimos
Gaspra
Phobos
Comets “small” icy highly eccentric orbitsall orbit inclinations
Comet Wild
Halley’s Comet
Comet Tempel 1
(“Deep Impact”)
Comets are found mainly in two regions of the solar system
UB313(1500 miles)
Kuiper Belt Objects
So how do we account for what we see in the solar system?