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Physics: Principles and Problems Solutions Manual 7 Copyright Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. 49. Explain the difference between a scientific theory and a scientific law. A scientific law is a rule of nature, where a scientific theory is an explanation of the scientific law based on observation. A theory explains why something hap- pens; a law describes what happens. 50. Density The density of a substance is its mass per unit volume. a. Give a possible metric unit for density. possible answers include g/cm 3 or kg/m 3 b. Is the unit for density a base unit or a derived unit? derived unit 51. What metric unit would you use to measure each of the following? a. the width of your hand cm b. the thickness of a book cover mm c. the height of your classroom m d. the distance from your home to your classroom km 52. Size Make a chart of sizes of objects. Lengths should range from less than 1 mm to several kilometers. Samples might include the size of a cell, the distance light travels in 1 s, and the height of a room. sample answer: radius of the atom, 5 3 10 2 11 m; virus, 10 2 7 m; thickness of paper, 0.1 mm; width of paperback book, 10.7 cm; height of a door, 1.8 m; width of town, 7.8 km; radius of Earth, 6 3 10 6 m; distance to the Moon, 4 3 10 8 m 53. Time Make a chart of time intervals. Sample intervals might include the time between heartbeats, the time between presidential elections, the average lifetime of a human, and the age of the United States. Find as many very short and very long examples as you can. sample answer: half-life of polonium-194, 0.7 s; time between heartbeats, 0.8 s; time to walk between physics class and math class, 2.4 min; length of school year, 180 days; time between elections for the U.S. House of Representatives, 2 years; time between U.S. presidential2 years; time between U.... View Full Document

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