Lesson 20
Central Force Motion; Reduced Mass, First Integrals of Motion

Name:faculty Section:M2 Start Time:13:43:22 Instructor:pate Course:355

1) Consider just two particles interacting via a central force, as in the case of a planet-star system. By thinking about the conservation laws, what general properties of central force motion can you find or describe? (Hint: The image should give you at least one idea or property!)



2) Suppose you are an astronomer observing a star and a newly found planet. By carefully observing the motion of the pair of objects, you can infer the mass of the planet if you know the mass of the star. You can get a feel for this by looking at the simulation on the physlet page. By observing the motion of the red mass-blue mass system (feel free to "Pause" and "Step" the simulation!), estimate the mass of the blue planet. Please be sure to state any assumptions you make and briefly explain the thought process you use to arrive at your estimate.

Note: To obtain your answer, you'll need to give another Physlet page a try. Important: This page will open in a NEW window, so you'll need to come back to THIS window (using the taskbar) to submit your preflight. Once again, if the physlet page does NOT load properly, please tell me what happens, including any error messages it displays, in the comments box below. Thanks. Click this link to get to the physlet page.



3) The reduced mass for a two particle system

  1. is closer to the larger of the two masses than the smaller
  2. is never more than half the largest mass
  3. is the same as the actual mass of the two particles
  4. is the mass of the two particles after they've been dieting



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