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Week 12 – Angular Kinetics Objectives

Week 12 – Angular Kinetics Objectives. Identify and provide examples the angular analogues of mass, force, momentum, and impulse. Explain why changes in the configuration of rotating airborne body can produce changes in the body’s angular velocity (conservation of momentum principle)

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Week 12 – Angular Kinetics Objectives

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  1. Week 12 – Angular Kinetics Objectives • Identify and provide examples the angular analogues of mass, force, momentum, and impulse. • Explain why changes in the configuration of rotating airborne body can produce changes in the body’s angular velocity (conservation of momentum principle) • Define centripetal force and explain where and how it acts • Solve quantitative problems relating to the factors that cause or modify angular motion

  2. Week 12 Angular Kinetics • Read Chapter 14 of text • Reference to figures in this presentation refer to the former text by Kreighbaum, which is on reserve • Self-study problems • Sample problems: • #1, p 459 – angular momentum calculation • #2, p 462 – conservation of angular momentum • #3, p 466 – angular impulse and change in angular momentum calculation • #4, p 469 – Angular analogue of Newton’s law of acceleration • Introductory problems, p 472: #5,6,7,9 • Homework problems (due Monday, November 28) • Additional problems, pp 473-474: #1,4,5 • Additional handout problem on moment of inertia

  3. Torque and Motion Relationships • Relationship between linear and angular motion • displacement, velocity, and acceleration (Fig H.1, p 315) • Angular analogue of Newton’s third law (F=ma), the instantaneous effect of a force or torque • Sample problem #4, p 469 • Torque = moment of inertia (I) X angular acc ( (Fig H.5-H.7) • What is torque? • What is moment of inertia ?(Fig H.3, p 319) • What is radius of gyration (Fig H.4, p 320) • Changing moment of inertia and radius of gyration in the body (Figures H.8 and H.9, p 323 and 324) • Calculations using a 3-segment system • Homework problem

  4. Instnataneous effect of net torque: Moment of Inertia Constant T = I What is torque?

  5. Instantaneous effect of net torque: Torque is constant What is rotational inertia, Or moment of inertia?

  6. Instantaneous effect of net torque: Ang acc constant

  7. What is Moment of Inertia? It is the resistance of a system to rotational acceleration, and is calculated at follows: Here, r (the radius of rotation) is equal to k (the radius of gyration), but that is not the case with extended bodies

  8. What is radius of gyration (k)? k 35 An indicator of distribution of mass about the axis. It is the distance from the axis to a point at which all the mass of a system of equal mass would be concentrated to have the MOI equal the original system. It is, then, the average weighted distance of the mass of a system to the axis. Equivalent systems k 35

  9. Determining MOI & K • Simple 3-segment system: • I = 3mi di2 = m1 d12 + m2 d22+ m3 d32 + . . . . . . .+ mi di2 • I = mk2 ; k = (I/m).5 • Irregularly shaped bodies But we can’t measure all of these small masses!

  10. Physical pendulum method of determining MOI and K • Suspend object at axis • Measure mass (m), and distance from axis to COM, r • Measure period of oscillation (T) • Moment of inertia (I) = T2 mr * .248387 m/sec • Radius of gyration (K) = ( I/m).5

  11. ChangingIandk in the human body

  12. ChangingIand k in the human body

  13. MOI around principal axes of human body in different positions

  14. Angular Momentum • What is angular momentum? (Fig I.4, p 329) • amount of angular movement: I  • Sample problem #1, p 459 • Impulse-momentum relationship - effect of force or torque applied over time • Linear: Ft = mv Rotational: Tt = I  • What is angular impulse? (Fig I.1, I.2, I.3, p 327-8) • Torque X time • Sample problem #3, p 466 • Conservation of angular momentum (Fig I.4, I.5, I.6 p 329-331) • Angular momentum is constant if net impulse is zero • Sample problem #2, p 462

  15. What is angular momentum (L)?

  16. Calculating Angular Momentum

  17. Conservation of AngularMomentum

  18. Conservation of Angular Momentum

  19. Conservationof angular momentum

  20. What is angular impulse?

  21. Angular Impulse: Mediolateral axis

  22. Angular Impulse around vertical axis

  23. Impulse-Momentum Relationship

  24. Torque-Angular acceleration

  25. Centripetal & Centrifugal forces Fc = mv2/r

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