PHY138 - Mechanics - Class 4 - Wednesday, September 21, 2005


“One of the biggest problems is how to state the problem. It's an old saying that the minute you can state a problem correctly you understand 90 percent of the problem.”

-- John A. Wheeler (physicist)

About Accessing MasteringPhysics

Some time late last week, subscribers to Rogers' internet service had access to MasteringPhysics blocked. Service was restored yesterday morning by at least 10:20 AM. Thus, for all students I have extended two deadlines:

  1. Pre-Class Quiz Chapts 2 - 4:
  2. MasteringPhysics Problem Set Chapts 1 - 4:

I am not extending the deadline for the Pre-Class Quiz Chapts 5 - 6: it is still due on Monday, September 26 by 10 AM.

Today's Class

Today we finished Chapter 2, discussed Chapter 3, and got over half way through Chapter 4. So our schedule as listed in the syllabus is slipping a bit, but not too much. (Yet.)

In-Class Questions

Although our treatment of friction will be only qualitative, we asked a question about it. Accessible with the button to the right; separate window. friction question

The correct answer to this question is 3: it can both slow things down and speed things up. The overwhelming majority of the class instead answered 1: friction slows things down. We will use this problem as our primary example of free body diagrams on Monday.

I also asked this question about the pace of the classes so far. force question

The results were:

Too slow: about 10% of the class
Too fast: about 70% of the class
Just right: about 20% of the class

Class Materials

Flash animation of adding two vectors. Theory of Intelligent Falling
Flash animation of adding three vectors. Theory of Intelligent Falling
Flash animation of subtracting two vectors. Theory of Intelligent Falling
Flash animation of vector addition by adding components. Theory of Intelligent Falling
Flash animation about unit vectors. Theory of Intelligent Falling
Pdf version of the PowerPoint on the side screens. Theory of Intelligent Falling
Today's Journal. Theory of Intelligent Falling


Suggested Problems

previous class The arrows let you jump to the previous/next class summaries. next class