Physics 9 The Solar System with Prof. D. Tytler Oct. 2000
Homework 3, was due Oct 19 in class
We encourage you to work together, to discuss the topics and solutions, but your answers must use all of your own words, calculations and diagrams.
You must not hand in work copied from someone else.
Please write down the code numbers of all in your study group.
The first question encourages you to think out an experiment. The others are revision.
1. Describe how you would measure the density of your body. It is hard to get your volume. One way is to use a bathtub full of water. Describe how this method, or some other method, works, what measurements are made, and how they are converted into a density. What value would you guess for the answer?
Density = mass/volume. The mass is easy, and is given by your weight. Scales are calibrated in pounds(lb) and kilograms(kg), and your weight in kg when on the surface of the Earth is the same value as your mass. You can get the volume by completely immersing yourself in water, in a tub, and noting the volume of water which you displace, for example from the increase in the level of the water.
2. Which types of meteorite are primitive and which are differentiated? GRADED
Primitive meteorites are those that have remained unchanged from the formation of the solar system; these are usually composed of stone. The most extreme are the carbonaceous chondrites. The iron and stony-iron meteorites are differentiated, which means that the planetary bodies they broke away from had surfaces of light material because the heavier elements had sunken to the middle. The question asks about meteorites, and requires examples.
3. Draw a diagram illustrating the phases for a moon of Saturn (any one - they will be the same). You may wish to give two diagrams, one showing the view from far above the orbit, and the other, the phases seen from Saturn. The goal of this question is revision of the concept of phases.
4. Why are eclipses not seen each month? The goal is revision of an important spatial concept.
This is because the Moon’s orbit is tipped 5º angle to the plane of the Earth’s orbit. So even when there is a New Moon, the moon isn’t always in front of the Sun our line of sight.
5. Explain, with words and show with a figure, the difference between the 3 major types of spectrum. Give for each a specific example (not writing just "gas"...). The goal of this problem is to practice extracting information from the book, and noticing the physical distinction between three relatively similar ideas. GRADED.
The first type of spectra discussed was an emission line spectrum, as produced by a gas. The spectral lines show the specific wavelengths at which atoms of the elements emit light.
The spectrum of a liquid or solid looks different because the atoms that make up the object are much close together than in a gas. Now the spectrum is continuous, meaning that the object absorbs a range of wavelengths rather than individual ones. An example is the reading of a planet that has no atmosphere.
The type of spectrum we get when looking at a planet is the continuous spectrum of sunlight reflected by the solid planet with downward jumps at the wavelengths of light absorbed by atoms in the atmospheres of both the sun and planet (if it has an atmosphere). This is called an absorption spectrum.
6. Describe the three main types of rock found on the Earth.
Igneous: rocks formed from the cooled lava, i.e. basalt, makes up 2/3 of Earth’s crust.
Sedimentary: different rocks that have been cemented together on the ocean floor, i.e. sandstone and limestone.
Metamorphic: igneous or sedimentary rocks that have been changed by pressure and heat inside the Earth, e.g. marble.
7. What is the difference between a rock and a mineral?
Minerals are pure (homogenous); they are made up of only one type of molecule. Rocks are inhomogeneous mixtures of minerals. The composition varies in different parts of the rock.
8. Kepler and Newton each contributed 3 laws to science. Name (enough to identify each, more than just the number, but no need for details) all six. Why are Newton's deemed so much more important? The goal of this problem is both memorization (learn these laws), and practice making value judgements.
Kepler’s Laws describe the orbital motion of the planets.
1. The orbits of the planets are shaped like ellipses. The Sun is at one focus and nothing is at the other.
Newton’s Laws explains why the planets move.
1. A body in motion will stay moving at a constant speed in a straight line unless acted upon by a force.
2. F=ma. A force is equal to the mass of the object it is working on, multiplied by its acceleration.
3. For every force there is an equal and opposite force.
You can derive Kepler’s laws from Newton’s, but not the converse. Newton’s Laws fully describe planetary motion, including details, such as tides, which are not found in Kepler’s laws. Newton’s laws also describe the motion of bodies in general, not just planets and stars in orbit.
9. Explain retrograde motion. Include 3 drawings:
a. how it appears from Earth
b. how it was explained in the geocentric model
c. how it is explained in the heliocentric model.
The goal of this problem is to practice making sketches which help explain phenomena. Notice how there are many ways to make a sketch, depending on what you are trying to show, and where you are located.