B. steel
A. distilled
3. (C) Copper is found in combination with other elements and also in a free state.
Nitrogen is a gas. Iron is seldom found in a free state, and aluminum occurs in combination with other elements in the earth's crust.
4. (D) When the su's rays strike a surface that is smooth, shiny, or light in color, the rays
are reflected. When the sun's rays strike a surface that is rough and dark, more of the rays are absorbed.
5. (A) In crop rotation, plants such as legumes are planted periodically to add nitrogen to the soil after other crops have exhausted it. None of the other methods returns minerals to the soil.
6. (B) A crowbar is a form of lever. By placing a crowbar over a support, you can exert pressure on one end and overcome resistance at the other. A crowbar can be placed on the surface of a rock as a fulcrum, for example, with one end under the edge of another rock, and then presed hard to dislodge the other rock.
7. (C) The lunar surface is darkened when the earth comes between the sun and the moon. This is caused by the fact that the shadow of the earth falls on the moon's surface.
(D) Barometric pressure decreases 1 inch for every 900 feet of altitude. The gas in the balloon expands because it enters regions of lower and lower pressure. Balloons being prepared for ascent are only partially filled with helium. The balloonist knows that the gas will expand and fill the balloon completely at higher altitudes.
17. (C) The analysis of radioactive material has given scientists an accurate estimate of the age of the earth.
18. (D) Coal deposits were formed when layers of giant ferns as well as other vegetation were compressed into layers of coal by the earth's movement. Its coal deposits tell us that Alaska must have had a tropical climate.
19. (A) The curve in the top of an airplane wing forces the air to flow faster over the top of the wing than below it. This faster flowing air results in less pressure above the wing. The principle behind this was first described by Bernoulli. In any flowing liquid, the pressure becomes less as the speed of the flowing liquid becomes greater.
20. (B) The lens focuses the light on the retina, which "records the image," sending impulses along the optic nerve to the brain. The cornea is the transparent tissue covering the eyeball. The pupil is the opening through which light enters the eye.
21. (B) When a water molecule is decomposed by electrolysis, it breaks up into hydrogen and oxygen; the ratio is two molecules of hydrogen to one of oxygen.
(D) FeSO, is a compound of three different elements- iron (Fe), sulfur (S), and oxygen (O). Hydrogen (H) is a separate element.
(CNitrogen is needed most by plants. They also have some need for phosphorus and potassium. Only traces of the other elements are needed by plants; they are not a major concern for companies that produce fertilizers.
(C) When an object is placed in water, it loses the exact same weight as the weight of the water it displaces. If two objects that are placed in water appear to lose the same
(A) A thermos is made with a vacuum between its double walls. In this vacuum, there are no molecules to receive the transfer of heat energy from the wall near the contents of the thermos. Thus, the vacuum prevents the loss of heat. Even though a storm window allows some air between it and the "year-round" window, it is the closest match to a thermos among the choices given.
(C) Calcium is a very important component of bones. Without it, the bones in our skeleton become brittle.
9. (D) The oxidation of the gasoline, which contains hydrogen, produces moisture.
There is also an oxidation of the carbon in gasoline, which produces carbon dioxide (not mentioned in the question) and traces of carbon monoxide. These traces can be dangerous when the engine of a car is running in a confined, poorly ventilated place.
10. (C) The telephone receiver has an electromagnet with a metal diaphragm mounted close to it. The metal diaphragm vibrates (moves back and forth) and reproduces the sounds spoken into the transmitter. The sound waves produced by the speaker's voice cause the transmitter to make the current in the wires weaker and stronger. These changes occur thousands of times per second. These changes in current affect the electromagnet in the receiver at the other end of the phone call. The receiving electromagnet affects its diaphragm strongly or weakly as the current changes. This in turn reproduces the sound waves made originally by the speaker's voice.
11. (D) Racio and light waves are two forms of electromagnetic radiation. In a vacuum all electromagnetic waves have the same speed —that is, the speed of light.
12. (C) The earthis atmosphere consists of a mixture of nitrogen (about 78 percent by vol-ume); oxygen (about 21 percent); carbon dioxide (about 0.03 percent); small amounts.
(C) All freely falling objects, regardless of their masses near the earth, fall toward the earth with equal acceleration. Any two objects at rest that begin to fall at the same instant will have equal velocities at the end of three seconds, or at any other time inter-val. Thus the ratio of their speeds will be 1:1.
(C) A falling barometer indicates the approach of low pressure and rising air. The rising of warm, moist air usually results in precipitation. We have reason to assume that the air is warm since we know that southeast winds come from lower latitudes where the air was warmed, picking up moisture when it passed over the Atlantic Ocean.
15. (A) Sand particles are visible and comparatively large. They can be caught in the small holes of a filter. Sugar, alcohol, and most inks form true solutions in which the particles are of molecular size, which will pass through filters.