Download Physics 127 Descriptive Astronomy Homework #10

Physics 127 Descriptive Astronomy
Homework #10 Key (Chapter 5)
Winter 2015
5-2. What is unique about the behavior of water compared to other common substances?
Water has several unique properties not exhibited by other common substances: (1) It can absorb or lose a great deal of
internal energy with a relatively small consequent temperature change. (In the language of physics, it has a large specific
heat). (2) Water is unusual in that it expands when it changes from its liquid state to its solid state, i.e., when it freezes,
therefore its solid state (ice) is less dense than its liquid state, so ice floats on water. With most any other common
substance the solid state is denser than and sinks into its liquid state. (3) Water molecules attract one another with greater
force than is the case with many other liquids. Thus water tends to stick together to form spherical droplets and to flow as a
continuous stream. (Physicists call this property surface tension.) (4) Water also is capable of dissolving an unusually large
number of other substances.
5-3. How does the greenhouse effect influence the temperature of the atmosphere? Which properties
of greenhouse gases in the atmosphere cause this effect?
The greenhouse effect causes the temperature of an atmosphere to be higher than it otherwise would be. A relatively high
transparency to visible light, but with a relatively low transparency to infrared radiation (like glass in a greenhouse or a car
window) causes the greenhouse effect to occur.
5-5. What are the different types of seismic waves? Why are seismic waves useful for probing Earth’s
interior structure?
Seismic waves come in two types: P (primary) or longitudinal waves, wherein the wave motion is back and forth in the
same direction as the wave is moving, which are transmitted throughout the earth’s interior and S (secondary) or
transverse waves, wherein the move motion is perpendicular to the direction in which the wave is moving, which are
not transmitted by the liquid core in the earth. By understanding not just what mediums transmit these wave types, but
also how P waves are refracted (bent) at the boundary between the earth’s mantle and liquid core and its liquid and
solid core, it is possible to map the earth’s internal structure, i.e., determine the locations of those boundaries.
5-8. Describe the process of plate tectonics. Give specific examples of geographic features created
by plate tectonics.
Plate tectonics is the gradual, but very slow, motion of large plates or segments of the earth’s crust, driven by the
comparably slow convective motion of the mantle beneath those plates. Plates collide and fold which causes the
formation of mountain ranges. Plates slide over or alongside one another which generates frictional heating, melting
and volcanism. Plates stick, then slip abruptly, causing earth quakes and associated faults and scarps. Plates separate,
sometimes allowing upwelling of material from beneath, causing features such as the mid-Atlantic ridge with its
associated volcanism and other geothermal activity, or the great rift valley of eastern Africa.