Presentation on theme: "Mon. March 7th1 PHSX213 class Class stuff –HW6W solution should be graded by Wed. –HW7 should be published soon –Projects ?? ROTATION."— Presentation transcript:
Mon. March 7th1 PHSX213 class Class stuff –HW6W solution should be graded by Wed. –HW7 should be published soon –Projects ?? ROTATION
Mon. March 7th2 Check-Point 1 You are using a wrench and trying to loosen a rusty nut. Which of the arrangements shown is MOST effective in loosening the nut?
Mon. March 7th3 Check-Point 2 You are using a wrench and trying to loosen a rusty nut. Which of the arrangements shown is LEAST effective in loosening the nut?
Mon. March 7th4 Torque The ability to cause angular acceleration, , is related to the applied force magnitude, applied force direction and the point of application of the force wrt the axis of rotation. = r F r F sin = r T F = r F T r F Axis of rotation
Mon. March 7th5 Rotational inertia (aka moment of inertia) is : A.the rotational equivalent of mass. B.the point at which all forces appear to act. C.the time at which inertia occurs. D.an alternative term for moment arm. Reading Quiz
Mon. March 7th7 Relating linear and angular variables a tan = r a R = v 2 /r = 2 r v = r
Mon. March 7th8 Rotational Kinetic Energy Consider a rigid body rotating around a fixed axis with a constant angular velocity, . K = (½ m i v i 2 ) = ½ m i ( i R i ) 2 = ½ (m i R i 2 ) 2 = ½ I 2 Where I is the rotational inertia (aka moment of inertia), I ≡ (m i R i 2 ) about that axis.
Mon. March 7th9 Rotational Inertia I ≡ (m i R i 2 ) For a continuous body of uniform density, I ≡ ∫ r 2 dm
Mon. March 7th10 Check-Point 3 An ice-skater spins about a vertical axis through her body with her arms held out. As she draws her arms in, her angular velocity: A) increases B) decreases C) remains the same D) need more information