ANSWERS TO STUDY QUESTIONS CHAPTER 1

1. e,b,d,a,c

2. (1)gravity - pulls all matter together on scales less than galaxy clusters; at larger scales gravitational forces are insufficient to compensate for expansion caused by big bang

    (2)electromagnetic - all matter is composed of atoms which almost always contain both positively and negatively charged particles. Opposite charges attract, while like charges repel. Chemical bonding, condensation, freezing, friction and muscle movement are but a few of the many actions that involve the interaction of these charged particles, that is - electrical forces.  Magnetic forces are created by charge in motion, such as when electrons move through a wire or when they spin as they orbit around the nucleus of an atom. Magnetic forces can be either attractive or repulsive. A compass needle lining up with the earth’s magnetic field is one example.

    (3)strong nuclear - forces which hold the nuclei of atoms together. Although these forces are incredibly strong, they are exerted over the smallest of scales - the size of atomic nuclei. Since atomic nuclei always contain positive charge, nuclei normally repel each other by electrical forces. However, if nuclei can get close enough together, the attractive nuclear forces will be stronger than the repulsive electrical forces and the nuclei will fuse. The resulting "crash" converts the nuclear potential energy that existed between the separated nuclei into kinetic energy, much like gravitational potential energy is converted to kinetic energy when an object falls towards earth. Immense pressures are needed to overcome the repulsive electrical forces and accomplish nuclear fusion. In nature such pressures are found only stars, but by implosion, humans have generated similar pressures in hydrogen bombs.

    (4)weak nuclear - about 1 billion times weaker than the strong force, it is very short range in its effect and responsible for many nuclear decay processes (i.e. radioactivity).

4. If you pull two magnets apart you must apply a force in excess of the the magnetic force (one aspect of the electromagnetic force) that holds them together and you must apply that force over some distance, therefore you are doing work. That takes energy, and since energy can neither be created nor destroyed, the energy used must be converted into a different form - in this case since the magnets have changed position within a magnetic field they have gained magnetic potential energy. When you let them go, the magnetic potential energy is converted to kinetic energy as they fly back together. When they hit each other the kinetic energy manifests itself as sound and heat (random molecular motion within the magnets).

5.  When energy is "used" it is converted to other forms of energy. For example: Food contains electrical potential energy stored in the position of it’s atoms relative to one another. When we digest and metabolize food we rearrange those atoms and ultimately convert their electrical potential energy into kinetic energy.

6. The most direct evidence for the Big Bang theory comes from the large scale expansion of our universe. The theory is also supported by background microwave radiation that is directionally uniform and of a temperature (2.726^o K) that corresponds closely to the predicted value.

7. Atoms as heavy as iron are formed by nuclear fusion in stable stars. Heavier atoms form by fusion also, but require more intense pressures produced by supernovas.

8. big bang, formation of first atoms, nebulae, condensation, first protostars, first stars, supernova, solar nebula, accretion, solar system, earth melts, density stratification, outgassing, oceans, biosynthesis

9. According to our textbook's 6th, 7th and 8th editions (the story is slightly different in earlier versions), as the solar nebula compressed into a disk, the inner part heated more than the outer. Lighter, icy "seeds" where able to condense where the nebula was cooler (outside) but not towards the interior where the hotter temperatures allowed only heavier, rocky seeds to condense. The rocky seeds accreted into the inner planets. Residual gases where later blown away when fusion first occurred in our sun. The resulting emission  of intense radiant energy, called the "solar wind", heated the inner planets much more than the outer planets. Most remaining gaseous compounds where driven away by the solar wind from the inner planets towards the colder outer planets.

10. meteorite bombardment, decay of radioactive elements, gravitational compression, solar energy

11. Density stratification changed the earth from a more or less homogeneous mix of meteorite-derived materials, to a planet consisting of compositionally distinct layers - the core, mantle and crust.

12. The solar wind "blew away" our early planet’s atmosphere. The rocky materials that were left behind later melted and released their trapped gases (mainly water and carbon dioxide) via volcanic activity. This "outgassing" did not release free oxygen. All oxygen was bonded to other elements, such as various metals in rocks, and carbon and sulfur in the atmosphere (CO₂, CO, SO₂). Free oxygen didn’t arrive until plants evolved which, through photosynthesis, could rearrange the atoms in water and carbon dioxide into carbohydrates and free oxygen.

13. There are two sources for the planet's ocean water. First, water outgassed by volcanoes collected as water vapor in the atmosphere. Upon cooling, atmospheric water vapor condensed, fell as rain, and collected in the low areas of the earth’s surface forming oceans. Second, a significant amount of water came for asteroids and comets after the earth formed. These vaporized as they entered the earth's atmosphere and that water later fell as rain.

14. The reactions involved in biosynthesis can not take place in the presence of free oxygen. Even though there are some anoxic environments on earth, any organic compounds that might be synthesized there would be gleefully metabolized by existing organisms long before they could evolve into new organisms capable of defending themselves.