Notes: Fri 9 Sept

Maps, continued

(handout: latitudinal geographic zones)
GIS: Geographic information systems: different mapping programs with applications in topography, zoning laws, flooding prevention, other demographics, etc.

Solar System Formation

Chemistry Review
atom: composed of protons (with a + charge) and neutrons (no charge) orbited by electrons(with a - charge). atoms with different numbers of neutrons are called isotopes. atoms with different numbers of electrons are called ions (i.e., the number of protons does not equal the number of electrons). When there is an excess positive charge (more protons than electrons), it is called a cation. When there is an excess negative charge (more electrons than protons), it is called an anion.

examples: hydrogen has 1 proton and 1 electron. A hydrogen isotope has 1 proton, 1 neutron and 1 electron. Helium has 2 protons, 2 neutrons, and 2 electrons. Lithium normally has 3 electrons, but if you take one away you get a cation with one excess positive charge.

Physics Review
Newton's Law of Gravitation: the force of gravity F=(GMm)/r2.
From this we can see that gravity depends heavily on the the product of the two masses. The sun is over 99% of the mass in our solar system, so it's the largest factor in the mass part of the equation. Also, gravity drops off as 1/r2,which means if you double your distance from the sun, you cut the force of gravity between you and the sun by 1/4.

Q: What is the effect of going farther away, but also getting more massive? Would those two effects cancel themselves out, leaving F the same everywhere?

plot of gravitational force vs. distance from sun
As you can see, the actual force between the sun and a planet is not entirely predictable from just looking at the masses and the distances. In these cases, the gravitational force does remain roughly constant within a range of about 100 Newtons (1 Newton=1 kg m/s2) except for Pluto. So it looks like the effect of increasing mass is in a way cancelled out by increasing the distance.

plot of gravity vs. distance from sun
This figure shows gravity, not gravitational force, of the sun at each planet. Gravity is a type of acceleration directed in toward the planet. Going back to your high school physics, you know that F=ma, where is acceleration. Well, for the gravitational force, F=mg (just plugging in g for a), so g=F/m. In other words, g is the force per unit mass that the sun exerts on a planet. But wait a second - we know what F is: it's (GMm)/r2. Therefore, g=(GM)/r2. Now that you know exactly what is being plotted here, it should not be a surprise that this curve drops off as 1/r2as mentioned in class.

Astronomical Distances
light year: the distance light travels in one year, which turns out to be about 9.454 trillion km. (You can figure this out for yourself by multiplying the speed of light (about 299,792 km/s) by the number of seconds in a year.)

Our place in the Universe
The universe is about 12 billion light years in "all" directions from us (we say "all" because we aren't really in the center).

The Sun is the driving force behind our atmosphere
Life on Earth depends on the atmosphere. The atmosphere is defined to be the veil of gases held by gravity. Our atmosphere has changed with time; it is not as it originally was. This is because the lighter elements, or volatiles, have already escaped, leaving heavier elements behind.

Our path around the sun
Our path of revolution about the sun is not perfectly circular, but slightly elliptical. (Remember that revolution refers to one body orbiting another body whereas rotation refers to a body spinning on its axis.)

The point where Earth is closest to the sun is called perihelion and usually occurs on January 3. Our distance then is about 147 x 106 km. The point where Earth is farthest from the sun is called aphelion and usually occurs on July 4, when we are about 152 x 106 km from the sun.

Notice that we are closest to the sun during our winter season. This indicates that distance from the sun is not the most important cause of our seasons. As we shall see later, the controlling factor in the seasons is the tilt of the earth's axis (though distance does play a minor role).

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