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1-1. The Scientific Method
  1. The scientific method consists of four steps:
    1. Formulation of a problem
    2. Observation and experiment
    3. Interpretation
    4. Testing the interpretation
  2. An initial scientific interpretation is called the hypothesis.
  3. A law describes a relationship or regularity between naturally occurring phenomena.
  4. A theory explains why a phenomenon or a set of phenomena occurs.
  5. Scientists often use models to simplify complex situations.
  6. Newton chose an oval called an ellipse as a model of the earth’s orbit.
1-2. Why Science Is Successful
  1. A scientific law or theory, if refuted by contrary evidence, must be modified or discarded.
  2. The work of scientists is open to review, test, and change.
  3. Science has provided an understanding of the natural world and a sophisticated technology.
  4. Scientific laws and theories are not accepted as "absolute truth" and therefore differ from belief systems.
1-3. A Survey of the Sky
  1. To an observer north of the equator, the position of the North Star, or Polaris, changes very little, and the whole nighttime sky appears to revolve around Polaris.
  2. The constellations are easily recognized groups of stars and are useful as labels for regions of the sky.
  3. The planets visible to the naked eye (Mercury, Venus, Mars, Jupiter, and Saturn) appear to drift in a generally eastward motion relative to the stars; however, each planet at times appears to head westward briefly, and its path across the sky resembles a series of loops.
1-4. The Ptolemaic System
  1. Ptolemy of Alexandria (2nd century A.D.) described the universe in the Almagest.
    1. The earth is the center of the universe.
    2. The sun, stars, and planets revolve around the earth.
    3. The orbits of the planets are circular.
  2. According to Ptolemy, the planets as they orbit the earth travel in a series of loops (epicycles).
  3. The ptolemaic system had the components of a valid theory:
    1. It was based on observation.
    2. It apparently accounted for known celestial motions.
    3. It made predictions that could be tested.
1-5. The Copernican System
  1. The ptolemaic system failed to make accurate predictions of planetary positions.
  2. Nicholaus Copernicus (1473-1543) developed a new theory of the universe:
    1. The earth and planets follow circular orbits around the sun.
    2. The earth rotates on its axis once every 24 hours.
    3. The earth’s rotation explains the daily rising and setting of celestial bodies.
    4. Irregular movements of the planets are a result of the combination of their motions around the sun and the change in position of the earth in its orbit.
  3. The copernican system was attacked by religious leaders and by other supporters of the ptolemaic system.
1-6. Kepler’s Laws
  1. Johannes Kepler (1571-1630), using Tycho Brahe’s improved measurements of planetary motion, found fault with the copernican system.
  2. Kepler’s calculations resulted in the discovery of three laws of planetary motion:
    1. The paths of the planets around the sun are ellipses with the sun at one focus.
    2. A planet moves so that its radius vector sweeps out equal areas in equal times.
    3. The ratio between the square of the time needed by a planet to make a revolution around the sun and the cube of its average distance from the sun is the same for all the planets.
  3. Kepler’s laws agreed with past observations of planetary positions and made accurate predictions of future planetary movements.
1-7. Why Copernicus Was Right
  1. There is direct evidence that the earth rotates and revolves around the sun.
  2. There is direct evidence for the motions of the moon and the other planets.
1-8. What Is Gravity?
  1. Isaac Newton’s (1642-1727) discovery of the law of gravity was dependent upon Copernicus’s model of the solar system.
  2. Gravity is a fundamental force.
    1. A fundamental force cannot be explained in terms of any other force.
    2. There are four fundamental forces:
      1. Gravitational
      2. Electromagnetic
      3. Weak
      4. Strong
  3. Gravity is thought to be a universal force because:
    1. Observed star systems and galaxies behave as if influenced by gravity.
    2. Matter appears to be the same throughout the universe; therefore, gravitational attraction must also be universal.
    3. There is no evidence that gravity is not universal.
1-9. Why the Earth Is Round
  1. The theory of gravity accounts for the earth’s shape; the earth is round because gravity squeezes it into a spherical shape.
  2. The earth is not a perfect sphere because its spinning motion causes it to bulge slightly at the equator and flatten slightly at the poles.
1-10. The Tides
  1. The law of gravity successfully explains the occurrence of the tides.
  2. The earth’s tides are the result of the gravitational attraction of the moon and the sun.
  3. Coastal areas experience two high tides and two low tides each day.
  4. The relative positions of the earth, sun, and moon produce different tides.
    1. Unusually high (and low) spring tides occur bimonthly when the moon and sun are aligned with the earth.
    2. Weak neap tides occur bimonthly when the sun and moon pull at right angles to each other in regard to earth.
1-11. The Discovery of Neptune
  1. Discrepancies in the predicted orbit of Uranus led to two hypotheses:
    1. The law of gravity is wrong.
    2. An unknown body is exerting a gravitational pull on Uranus.
  2. Calculations based on the law of gravity predicted the position of an unknown body.
  3. The prediction was tested, resulting in the discovery of Neptune.
1-12. The SI System
  1. A measurement consists of a number and a unit or standard quantity.
  2. Scientists and almost all nations use the SI or International System of measurement.
    1. Examples of SI units include:
      1. Meter (m) for length
      2. Second (s) for time
      3. Kilogram (kg) for mass
      4. Joule (J) for energy
      5. Watt (W) for power
    2. Units in the SI are based on subdivisions and multiples of 10.

The Physical Universe, 11eOnline Learning Center

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