1. Acceleration - rate of change of velocity (speed or direction), occurs any time an unbalanced force is applied

2. Aphelion point of a planet’s orbit when it is at its greatest distance from the Sun

3. Astronomical Unit average distance from the Earth to the Sun

4. Center of Mass average position in space of a group of massive bodies

5. Centripetal Force force that pulls an object into a curved path

6. Eccentricity - measure of the flatness of an ellipse

7. Ellipse elongated circle shape of orbits

8. Escape Velocity speed required for an object to escape gravitational pull

9. Focus point an object orbits (elliptically)

10. Force a push or pull primarily gravity

11. Gravitational Constant - constant of proportionality in the law of Universal Gravitation

12. Gravitational Field field created by object with mass, determines its influence on other objects

13. Gravitational Force the attractive force a massive object has on all other massive objects

14. Gravitational Slingshot use of gravitational pull of massive object to increase velocity of a passing satellite

15. Heliocentric - solar system model with Sun at the center

16. Hyperbola - geometric shape of an unbound orbit

17. Inertia - tendency of objects to resist acceleration, Newton’s 1st Law

18. Inverse-Square Law strength of field decreases with square of the distance

19. Kepler’s Laws of Planetary Motion three laws which summarize the motion of the planets

20. Major axis - the long axis of an ellipse

21. Momentum - a measure of the inertia of a body, mass X velocity

22. Newtonian Mechanics - basic laws of motion, postulated by Newton

23. Parabola - shape of orbit with just enough energy to escape gravitational field

24. Perihelion - closest approach to Sun in an orbit

25. Radar - radio detection and ranging, waves are bounced off an object and timed to find distance

26. Renaissance - historical period with a rebirth in scientific inquiry

27. Semi-major Axis average distance of a planet from the Sun

28. Unbound - an orbit in which the satellite will never return to the object it orbits

29. Weight - a measure of the gravitational pull between two objects

30. 1. Why did the Ptolemaic picture of the universe survive for so long? Traditionalists were reluctant to give up the belief that the Earth was the center of the universe.

31. 2. What was the great contribution of Copernicus? Placing the Sun at the center of the solar system.

32. 3. What was Copernicus’ major motivation for introducing the heliocentric model of the universe? Copernicus wanted to simplify the view of the solar system.

33. 4. When were Copernicus ideas finally accepted? Late 1600s to early 1700s.

34. 5. What is the Copernican principle? The Earth is not special in a cosmological sense.

35. 6. What discoveries of Galileo helped confirm the views of Copernicus? He found moons that orbited Jupiter. He saw phases of the planet Venus.

36. 7. What was Kepler’s contribution to astronomy? Kepler’s laws of planetary motion. 1. planets’ orbits are elliptical 2. planets sweep out equal areas of the ellipse in equal periods of time (move faster closer to the Sun) 3. square of a planet’s orbital period is proportional to the cube of its distance from the Sun

37. 8. What did Kepler use as the basis for his ideas? The observations of Tycho Brahe.

38. 9. Do Kepler’s laws let us specify the actual distances between orbits of the planets and thereby the scale of the solar system? Kepler’s laws tell relative distances, not actual distances.

39. 10. How can radar be used to find the distance between Earth and Venus? INFERIOR CONJUNCTION SUPERIOR CONJUNCTION The sum of the two distances divided by two is one astronomical unit.

40. 11. What is inertia? Give one example. Objects resist acceleration. Seat belts keep you from slamming through the windshield.

41. 12. Consider the gravitational interaction between Earth and a baseball thrown into the air. If the force of gravity is acting on both of them, why does the baseball move toward Earth and not Earth toward the baseball?

42. F = m X a F on each object is equal, but m for the Earth is huge while m for the baseball is very small. That makes a for the Earth very small while a for the baseball is huge.

43. 13. Why would a baseball go higher if it were thrown upward from the surface of the Moon? The mass of the Moon is less than Earth’s so the acceleration due to gravity is less. Therefore, it would take the ball longer to lose its velocity.

44. 14. Why can the motion of a planet around the Sun be described as a tug-of-war? The Sun pulls on the planet and the planet pulls on the Sun. This makes them each orbit a common center of mass.

45. 15. Do planets orbit the center of mass of the Sun? No, a planet and the Sun orbit a common center of mass.