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Physics LibreTexts

1.30 Questions Chapter 1

Intended for all audiences, this textbook is an introduction to the nature of the universe. Use it to research or review our solar system, stars, galaxies, and the history of the universe. Each chapter has a set of corresponding homework questions.

Questions Chapter 1


  1. Evaluate the scientific reliability of each statement below, and decide how reliable each argument is.
    1. Einstein said that mass can be converted to energy, so it must be true.
    2. A modern-day cult stores food under pyramids because its members believe, without any tests, that pyramids have supernatural powers to preserve things.
    3. At a trial, a lawyer pays expert witnesses to testify in favor of her side of the case and moves to have evidence favoring the other side thrown out.
    4. At a medical conference, doctors discuss the effectiveness of a certain drug. Seven out of ten medical researchers on the panel report positive tests that the drug works. One finds negative results, and two find that their patients’ improvement is no better than random, within the error bars.
    5. The drug manufacturer in case (d) states in its advertising that the product is “proven effective” because a majority of doctors find that the drug works.

  2. Discuss the difference(s) between a working hypothesis and a theory.

  3. Ten scientists want to measure a particular quantity, but one of them claims to have measuring equipment that is much more accurate than the equipment of the others. Which strategy would produce the “best” measurement, and why?
    1. Let only the scientist who claims to have the most accurate equipment make the measurement.
    2. Let the scientist who claims to have the most accurate equipment and one of the others make measurements, and then compare the two answers.
    3. Let all 10 make the measurement and then gather to compare and discuss the results.
    4. Let only the nine scientists with ordinary equipment make measurements, and take an average of their nine answers.

  4. What is the basis for our belief in causality, the idea that every action has a cause? How would it affect the value of the scientific method if this were not true and events in the everyday world happened spontaneously without any prior cause?

  5. Evaluate the reliability of these various types of evidence for identifying UFOs as alien spacecraft.
    1. A series of photographs published in a weekly newsmagazine.
    2. A sighting of what was believed to be a metallic disk by a close relative of yours.
    3. A similar report by a member of the U.S. President’s Cabinet.
    4. A piece of very dense metal found near scorch marks in a wheat field somewhere in the Midwest.
    5. A report from a friend in the military who says he heard rumors from several officers of frozen aliens being kept at an Air Force base in Nevada.
    6. Hundreds of independent visual reports and a series of 56 photographs taken in sequence on the same evening in different towns along a line from Oregon to Nevada, showing a formation of three brilliant objects moving toward the southeast at a calculated rate of 650 miles per hour (mi/h). The objects are so small or high that best photographs show them only as blurry triangular shapes.
    7. A detailed account of an abduction by aliens, recounted on a daytime TV talk show.
    8. What more would you want to know in each situation to evaluate the evidence? Can you think of a hypothesis other than alien spaceships that might account for each report? Give examples of the minimum evidence you would demand before believing the hypothesis that some UFOs are alien spacecraft.

  6. Critique the following statements from the perspective of the scientific method, explaining what, if anything, is wrong with each one or what you would like to know in order to clarify each one.
    1. “Nine out of ten scientists believe in the big bang model for the creation of the universe, so I believe it, too.”
    2. “Nine out of ten scientific reports published in an international medical journal find that a certain food additive causes cancer in mammals and advise against using it, so for the time being I’m going to try to avoid using it, although I recognize that future tests may give different answers.”
    3. “My favorite talk show host says that a certain food additive causes cancer, so I’m going to stop using it.”
    4. “Team, I want you to go out there and give 110 percent.”
    5. “The cake probably weighs 2.3461 kilograms (kg).”
    6. “Wind is caused by trees waving their branches.”
    7. “Lung cancer is caused by smoking.”
    8. “There is no chance that Los Angeles will suffer a major destructive earthquake within the next 10 years.”

  7. How would you design a scientific experiment to test the existence of telepathy (the ability to transmit thoughts without verbal communication)?

  8. To how many significant figures do you know your weight? Your height? Your bank account (or the amount of change in your pocket) at any given time? To how many significant figures do you think we know the population of the planet at any particular time? Discuss the sources of uncertainty in each case. Why do modern scientists often need to measure more significant figures than in these cases to make progress?

  9. Conduct a simple experiment using estimation.
    1. Find some spherical beads or marbles of one size and put them in a box. Measure the size of one of the spheres.
    2. Discuss a method for estimating the number in the box without counting them. Try to think first of a simple method, and then try to think of ways you might refine it by allowing for more details of the situation. Hint: Discuss whether the spheres fill all the space. Do they stack in regular order?
    3. Make the estimate by as many methods as you can and then count the marbles. Compare the results. By what percentage were you in error? If you had more than one method, was the error less for your more sophisticated method(s)?
    4. Now use the techniques you have learned to make a more accurate estimate of the number of times the Earth would fit inside Jupiter.

  10. Here are some quantitative “measurements” of various bits of information. Arrange them on a list, in order from least accurate to most accurate.
    1. A book is measured as 124 mm long, using a meter stick marked off in units of 1 mm.
    2. Someone’s birth month is known, but not the actual day of birth.
    3. A magnetic field is measured to have a strength of 560 ± 17 gauss (G).
    4. The number of grains of sand on a beach is estimated as 1012.
    5. An aerial photograph of an open-air concert leads to a crowd size estimate of 40,000 to 60,000 people.