Physics121C_L21

# Physics121C_L21 - Physics 121C Mechanics Lecture 21...

This preview shows pages 1–9. Sign up to view the full content.

Physics 121C - Mechanics Lecture 21 One-Dimensional Rotation November 24, 2004 John G. Cramer Professor of Physics B451 PAB [email protected]

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
November 24, 2004 Physics 121C - Lecture 21 2 Announcements Homework Assignment #6 has been posted on Tycho and is due tonight, Wednesday, November 24 at 9:00 PM. The last question of the last problem (“Space Explorer”) of Homework Assignment #6 on Tycho does not make sense. It will not be counted. Do not attempt it. However, be sure to answer the first three questions of the problem.
November 24, 2004 Physics 121C - Lecture 21 3 8 15-Nov-04 17 Work 11.1 to 11.5 Work and Energy Angular Acceleration 17-Nov-04 18 Energy Conservation 11.6 to 11.9 19-Nov-04 19 Universal Gravitation 12.1 to 12.5 9 22-Nov-04 20 Orbits & Rotation No Tutorials Make-up Labs 24-Nov-04 21 1-D Rotation 26-Nov-04 HOLIDAY - 10 29-Nov-04 22 Energy & Angular Mom. 13.7-13.10 Angular Momentum Simple Harmonic Motion 01-Dec-04 R3 Review & Extension - 03-Dec-04 EXAMINATION 3 - Chapters 11-13 Lecture Schedule (Part 3) You are here!

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
November 24, 2004 Physics 121C - Lecture 21 4 Plotting α and ϖ The angular acceleration α is the rate of change of the angular velocity ϖ . If the angular acceleration α and the angular velocity ϖ are plotted vs. time t , then α is the slope of the ϖ vs. t curve, and ∆ ϖ = ϖ ( t f 29-ϖ (t i ) is the area under the α vs. t curve in the time interval between t i and t f . d dt ϖ α= f i t t dt α =
November 24, 2004 Physics 121C - Lecture 21 5 Example : A Rotating Wheel Figure (a) shows the angular velocity ϖ vs. time t. What rotational behavior does it describe, and what is the angular acceleration α ? The angular velocity ϖ is positive, so the plot describes a counterclockwise rotation that increases from t=0 to t 1 , remains constant from t=t 1 to t 2 , and decreases to a halt from t=t 2 3 . Figure (b) shows the corresponding angular acceleration α .

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
November 24, 2004 Physics 121C - Lecture 21 6 Rotational and Linear Kinematics α is constant a is constant
November 24, 2004 Physics 121C - Lecture 21 7 Example : A Rotating Crankshaft A car’s tachometer indicates the angular velocity ϖ of the crank shaft in rpm. A car stopped at a traffic light has its engine idling at 500 rpm. When the light turns green, the crankshaft’s angular velocity speeds up at a constant rate to 2500 rpm in a time interval of 3.0 s. How many revolutions does the crankshaft make in this time interval? 500 rpm (2 rad/rev)/(60 s/min)=52.4 rad/s i ϖ π = × 2500 rpm 5 262.0 rad/s f i = = = 2 (262.0 rad/s 52.4 rad/s) 69.9 rad/s (3.0 s) f i t α - - = = = ( 29 ( 29 2 1 2 2 1 2 2 0 (52.4 rad/s)(3.0 s) (69.9 rad/s ) 3.0 s 472 rad 75 rev f i i t t θ = + ∆ + = + + = =

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
November 24, 2004 Physics 121C - Lecture 21 8 Clicker Question 1 The fan blade shown is slowing down. Which option describes α and ϖ ?
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 11/29/2009 for the course PHYSIC 1D03 taught by Professor Dr.reid during the Spring '09 term at McMaster University.

### Page1 / 34

Physics121C_L21 - Physics 121C Mechanics Lecture 21...

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online