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25 Cards in this Set
- Front
- Back
center of mass
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The balance point of a body or system of masses. The point about which a body or system of masses rotates in the absence of external forces. (p. 69)
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circular velocity
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The velocity an object needs to stay in orbit around another object. (p. 68)
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closed orbit
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An orbit that returns to the same starting point over and over. Either a circular orbit or an elliptical orbit. (p. 69)
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deferent
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In the Ptolemaic theory, the large circle around Earth along which the center of the epicycle was thought to move. (p. 51)
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eccentricity, e
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A number between 1 and 0 that describes the shape of an ellipse. The distance from one focus to the center of the ellipse divided by the semimajor axis. (p. 59)
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ellipse
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A closed curve around two points called the foci such that the total distance from one focus to the curve and back to the other focus remains constant. (p. 58)
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epicycle
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The small circle followed by a planet in the Ptolemaic theory. The center of the epicycle follows a larger circle (the deferent) around Earth. (p. 51)
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equant
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In the Ptolemaic theory, the point off center in the deferent from which the center of the epicycle appears to move uniformly. (p. 51)
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escape velocity
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The initial velocity an object needs to escape from the surface of a celestial body. (p. 69)
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geocentric universe
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A model universe with Earth at the center, such as the Ptolemaic universe. (p. 50)
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geosynchronous satellite
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A satellite that orbits eastward around Earth with a period of 24 hours and remains above the same spot on Earth's surface. (p. 68)
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heliocentric universe
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A model of the universe with the sun at the center, such as the Copernican universe. (p. 49)
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hypothesis
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A conjecture, subject to further tests, that accounts for a set of facts. (p. 59)
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inverse square relation
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A rule that the strength of an effect (such as gravity) decreases in proportion as the distance squared increases. (p. 66)
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mass
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A measure of the amount of matter making up an object. (p. 66)
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natural law
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A theory that is almost universally accepted as true. (p. 59)
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neap tide
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Ocean tide of low amplitude occurring at first- and third-quarter moon. (p. 71)
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open orbit
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An orbit that carries an object away, never to return to its starting point. (p. 69)
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paradigm
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A commonly accepted set of scientific ideas and assumptions. (p. 54)
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parallax
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The apparent change in position of an object due to a change in the location of the observer. Astronomical parallax is measured in seconds of arc. (p. 50)
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retrograde motion
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The apparent backward (westward) motion of planets as seen against the background of stars. (p. 50)
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semimajor axis, a
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Half of the longest diameter of an ellipse. (p. 58)
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spring tide
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Ocean tide of high amplitude that occurs at full and new moon. (p. 71)
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theory
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A system of assumptions and principles applicable to a wide range of phenomena that have been repeatedly verified. (p. 59)
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uniform circular motion
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The classical belief that the perfect heavens could only move by the combination of uniform motion along circular orbits. (p. 50)
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