Physics 105, Fall Term, 2009

Reading: Chapters 7.1-7.3

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1) Rotational motion is really the same as linear motion, with the same equations exchanging linear terms with rotational terms.

2) The linear motion of an object at any given point is the tangent to the point of the circle it is on.

A lot of people are intimidated by rotational motion; however, you only need to use the same equations as with linear motion. The only change is exchanging things like distance with angle, velocity with angular velocity, and acceleration with centripetal acceleration. To see this conceptually, go to: http://phet.colorado.edu/sims/rotation/rotation_en.jnlp and click on the 'Rotational' tab at the very top of the applet. There are boxes which you may type in values for the variables you are looking at. You will also need to hit the 'Clear' button below these boxes between each activity. Change the graph options to showing the angle, angular velocity, and angular acceleration by clicking the 'θ, ω, α' bubble.

With θ and α both at zero, change the angular velocity to 30 degrees/second and press the 'Go' button directly below where you changed the value. Which best represents the relationship of the angular position of the ladybug compared to time?

Always 0 Constant, but not 0 Linear Exponential

Which best represents the relationship of the angular velocity of the ladybug compared to time?

Which best represents the relationship of the angular acceleration of the ladybug compared to time?

Change the angular velocity to 5 degrees/second and the angular acceleration to 30 degrees/second^{2}. Which best represents the relationship of the angular position of the ladybug compared to time?

Now change the graph settings to show linear velocity by clicking the 'θ, ω, v' bubble. Start with the ladybug close to the center of the rotating platform and change the angular velocity to 90 degrees per second and press 'Go'. While the platform is spinning move the lady bug out toward the edge of the platform. How does this affect angular velocity?

Increases angular velocity Decreases angular velocity Angular velocity remains the same

How does this affect linear velocity?

Increases linear velocity Decreases linear velocity Linear velocity remains the same

What is the direction of the velocity vector?

The direction of linear velocity is always tangent to the circle that the ladybug moves along.

The comments entered in these last two boxes go into a big anonymous data file that I will use to guide the lectures of the day. That means two things:

1) If you have a specific question or concern and would like an individual answer you will need to come by the office or send an email. 2) If you really want to get an anonymous comment to me before the lecture, it must be submitted before 11am that day.

Was there anything that you didn't understand in the reading assignment? What was confusing to you?

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