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M11 Revised Lecture
Friday, March 01, 2013
5:47 PM
Slides
Notes
Title
Four Forces:
Gravitational Force (this module)
Electromagnetic Force (next module)
Strong Force and Weak Force (module 13)
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Gravitational Force
This one is the easiest to experience of the
four forces. Sir Isaac Newton was the first
scientist to realize that the gravity that
makes something drop is the same as what
causes planets to orbit the sun.
-----------------------
Universal Law of Gravity
The equation that he came up with for the
Universal Law of Gravity is beyond your
abilities at this point, but you can learn his
3 general principles:
1.
All objects with mass are attracted
to each other
2.
The force of attraction is
directionally proportional to their
mass.
3.
The force is inversely proportional
to the square of the distance
between the objects
-----------------------
Then there is a Math Pag
e ...
Force and Circular Motion
Centiptdal Force:
Force that is always directed perpendicular
to the velocity of the object.
Centripetal acceleration:
Circle at a constant speed, but because the
direction keeps changing it actually works
out to be acceleration.
1.
Circular motion requires
centripetal force
2.
The larger that force, the faster the
object travels in a circle
3.
The larger centripetal force, the
smaller the circle of motion.
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Lab 11.1
Solar System
Eliptical orbit plus axis tilt equals season.
INNER:
Mercury is at 1/90
Venus is at 2/90 (warmest, surprise! - thick
atmosphere lots of CO2)
Earth is at 3/90
Mars is at 5/90
OUTER. Massive Gas Planets
Jupiter, just beyond 15/90 (rings)
Saturn would be at 30/90 (rings)
Uranus just before the 60/90 (rings)
Neptune near 90/90
Objects orbit planet = satellite (moon)
Perturbations - variations in the orbit often
caused by other planets that are also
orbiting. Neptune was found because of
the perturbation of the orbit of Uranus
Asteroids and Meteors:
Pictured is the meteor that was such a
surprise in Russia. There was an asteroid in
February 2013 that was closer than many
satellites but it was not expected that
anything would hit the planet. Surprise.
Just before the main asteroid came
through the same day Russia was hit with
this one.
When is it an asteroid and when a meteor?
What is a meteorite?
-----------------------
Comets and Meteors
Coming Soon - Comets
Comet C/2011 L4 (PANSTARRS) in March
ISON is a sungrazer that will been seen
October through January 2013
C2013 A! may impact Mars October 2014
and we will be in the debris field from
impact on 1st of October 2015
Gravity works on comets as well. Comets
have the nickname of dirty snowballs since
they are mostly ice, dirt, and dust. The ice
isn't just frozen water though, it is frozen
carbon dioxide, ammonia, and methane.
Comets are typically less than 150 miles in
diameter and orbit our sun as the planets
do but in a very elliptical orbit. They get a
brilliant tail when they are close to the sun
because the sun's heat sublimes the frozen
material instantly to a gas skipping the
liquid phase because there is so much heat.
This emits light.
The brightest part is the nucleus of the
comet which is the head. The fuzzy looking
halo around the comet is called the coma.
The tail always points away from the sun
because it is formed not from velocity but
from the solar wind that pushes out from
the sun.
The heat from the sun caused the comet to
disintegrate more and more with each pass
until they disappear altogether.
Short period comets take 3 to 9 years to
make an orbit and they seldom go any
further away from the sun than Jupiter.
These come from the Kuiper Belt which the
Huble telescope confirmed existed in 1992.
Collisions in this belt will cause material to
start falling toward the sun becoming a
comet.
Long orbit comets go further out than the
planets. Haley's Comet and Hale-Bopp are
of this type.
The last category is the very long-period
comets. They go to the outer edges of the
solar system and take 5,000 or more years
to make their orbits. The theory is that
these come from the Oort cloud. The Oort
cloud was proposed in 1950 by a Dutch
scientist. I bet you can guess what his last
name was. Yes, Oort.
---------------------------
What Causes Gravitational Force?
In 1916 Albert Einstein proposed his
General theory of Relativity. One of the
byproducts was explaining what causes
gravity. He explains that space actually
bends in the presence of an object. His
math equations explained Mercury's orbit
perfectly. He also predicted that light too
bends. Scientists were able to prove that
light does indeed bend when it passes a
star.
Here is an experiment to help you
understand the bending and how it
influences motion in space.
Lab 11.3
There is a competing theory, however. In
this theory, objects exchange something
called gravitons. They have to do this in a
short period of time, so only when they are
close or large can they do it in time. While
we have no proof of this theory working on
a large scale, it does seem to explain the
weak force. We will be talking about this in
an upcoming lesson.
It is even possible that both theories are
true and they work together. The bending
of space causes the gravitons to get close
enough to be exchanged, for instance.
History of the View of Our Solar
System
Geocentric - Greek, 2nd century:
Ptolemy,
Heliocentric - Renaissance, 16th century:
Copernicus 1543 (4 major moons of Jupiter
and rings of Saturn, too)
Galileo 1609
Brahe and Kepler at work on it at the same
time - Kepler's Laws
Newton -