Worksheet #6 Chapter 6 – Circular Motion, Orbits, & Gravity Terms, Definitions, Vocab Uniform Circular Motion Frequency Period Centripetal Force Law of Gravity Orbits v2 ac r f 1 T g planet 2 r Gm1m2 2 fr G 6.67 1011 Nkgm F1,2 F2,1 T r2 GM planet GM 4 2 3 2 v T r 2 r R planet GM v 2 2 Skills & Concepts 1. Chapter 6 starts by re-defining centripetal acceleration, which is first introduced in section 3.8, and then uses that acceleration term with Newton’s 2nd Law, which is discussed all over chapters 4&5, but most focused in section 5.2. It is worth reviewing these sections as part of your preparation for this chapter. 2. If a turn-table is spinning at a frequency of 45 rpm (revolutions per minute), what is its period of rotation in seconds? 3. What direction does the net force point for an object experiencing uniform circular motion? 4. What direction is the force by the Earth on the Moon? Should this scare you? 5. There are two constants defined by the letter G, one capital and one lower-case. Which of them is the same on Mars and on Earth? 6. When studying the orbit equations presented in section 6, pay particular attention to which mass the variable ‘M’ [Capital M] represents. 7. If the Moon were replaced with a baseball, how would its orbital period and velocity change? 8. If the Earth were replaced with a baseball, how would the Moon’s orbital period and velocity change? Example Problems Fill in the blank boxes for each problem. The boxes on the left contain mathematical steps, while the boxes on the right contain brief explanations of the step Example 6.2 List Known and Desired Quantities Convert given quantities into desired Units Solve for Period v 2 fr 2 (60 Hz )(0.125 m) v 47 ms Use the above value to solve for acceleration How does the acceleration you found compare to the gravitational acceleration? If the saw blade was bigger (larger radius) would the same frequency produce a larger or smaller speed? And a larger or smaller centripetal acceleration? Example 6.7 List Known and Desired Quantities Fnet y ma y NTrack ,Car WEarth ,Car 0 NTrack ,Car mg Use Newton’s 2nd Law I the horizontal direction, and the definition of centripetal acceleration, to create an expression that includes the velocity of the car Write an expression for the maximum static friction force on the car Use the above expression, and the values given to solve for the maximum speed Does this maximum speed depend on the mass of the car? If we instead took a wider, 40-m radius turn, how much larger would the maximum speed be?