Transcript Tidal Forces

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 PhobosGrunt is scheduled to launch and land on Phobos next year.
Kirkwood Observatory Open House
Out-of-class Activity:
Every clear
Wednesday evening
for the rest of the
semester.
Check website for
details.
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?
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mass – the amount of matter in an object
weight – a measurement of the force due to
gravity acting upon an object
W = mg
F = ma
(weight)
When in free-fall, you
still have weight!
“weightless” is a misnomer
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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).
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Now look at what happens when we measure the forces
relative to the center of the Earth.
Tidal Friction
Tidal Friction
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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
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…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.
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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.
Nine planets
Need to understanding the similarities and
differences between the planets, moons,
asteroids, & comets
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
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Size – “smaller”
Location – closer to Sun
Composition – rocky/metallic
Temperature – hotter
Rings – none
Rotation rate – slow
Surface – solid
Atmosphere – “minimal”
Mars
Earth
Venus
Mercury
Terrestrial Planets
Mercury
No moons
Venus
No moons
Earth
Mars
One moon
Two moons
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Saturn
Neptune
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Size – “larger”
Location – farther from Sun
Composition – gaseous (mostly H,He)
Temperature – cold
Rings – ubiquitous
Rotation rate – fast
Surface – not solid
Atmosphere – substantial
Uranus
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Jupiter
Jovian Planets
Jupiter
>61 moons
Uranus
> 27 moons
Saturn
> 31 moons
Neptune
> 13 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
Asteroids
small
Rocky
Odd-shapes
nearly circular orbits
orbit planes are near Ecliptic Plane
orbits in inner part of solar system
The
“asteroid belt”
Asteroids
Gaspra
Deimos
Mars’ moons and the
asteroid Gaspra
Phobos
Comets
“small”
icy
highly eccentric orbits
all orbit inclinations
Comet Wild
Halley’s Comet
Comet Tempel 1
(“Deep Impact”)
Comets are found mainly in two regions of
the solar system
Kuiper Belt Objects
UB313
(1500 miles)
So how do we account for what we
see in the solar system?