Rolling worksheet

Here is the worksheet from class on Wednesday.

Test 3 Grades

Test 3 grades are posted on WebAssign. The average was 49%. Here is the grade distribution:

screenshot_21

Chapter 7 Problem 12 - its not my fault

I have re-examined chapter 7 problem 12. I know why my answers do not agree - it is because the problem is worded poorly. This WebAssign problem is adapted from problem 59 in Chapter 7 of your text. In that problem (in the text) it refers to example 7.11 (on page 242). The misunderstanding is that I read the problem to say that mass 1 was ONLY moving in the y-direction after the collision. They meant to say that the y-component of velocity was v1.

The basic idea that the change in momentum for mass 1 is equal and opposite to the change in momentum for mass 2.

Since there was a mistake - here is a more detailed solution.

Equations for Test 3

For the next test, I will allow you to create your own equation sheet. You may use one page and write equations on it (as many as you like). You must turn this in with the test and it can not contain worked out problems or other things.

More practice problems

I said that I would post the practice problems from class today. Here they are.

I also said that I would post the solutions to the last worksheet. I will post these outside my door. But a note:

I hope you do not believe that by merely looking at the solutions, you will perform well on the test. To understand this material, you have to work at it. That includes doing the homework and these practice sheets. A surprising number of you have not submitted the homework (or have not submitted many times). I would recommend you do the homework. If you get stuck, seek help (I am here).

In class worksheet

Here is the worksheet that we used in class on 3/21/07 (it is pdf)

Springs Applet

Here is a great applet for springs. I am going to use this in class. If you want to play with it, make sure you use 1/16th time and show the energy graph.

Quizzes on Friday

I will now start giving weekly quizzes in class. There will be a quiz at the beginning of class each Friday. Quizzes are optional and I will take the higher of your quiz average or your lowest exam. There will not be any make-up quizzes. This Friday's quiz will be on Chapter 6

Physics Project

Well, I have put up information on the physics project - as discussed in class. The project is optional and will replace your lowest test grade (unless your lowest test grade is greater than your project grade). I will add an assignment in WebAssign for you to submit your project. Feel free to contact me with any questions about this project.

Course Changes

I opened a forum in WebAssign (yes, it has a forum in the communications section) so that we can discuss future strategies in the class. I am open to new ideas to help you succeed in the class, but there are some parameters that I must follow.

First, I can't just give you an "A". I don't really like grades, I think they get in the way of real learning, but part of my job is to evaluate your understanding of physics.

Next, I still have to evaluate your understanding of physics. I plan to use tests to do this, but if you have other ideas, I will be happy to listen. I can think of two possible alternatives to evaluate you, oral exams and perhaps a project. Oral exams would help out those that have trouble in the in-class environment. A project would be some longer-term task that perhaps could count equal to one test grade.

The last parameter is the topics covered. This is a service course for more than one major. Other departments (or accrediting agencies) have determined that you need to take physics. They made this determination based on the general description in the catalog. Thus, I can not significantly alter the content to be addressed. Also, if you plan to transfer your credit for this class to another institution, they expect certain topics to be covered. The list of chapters described for each test will have to be covered.

Test 2- Retest

I will post the Test 2 retest scores on WebAssign sometime this weekend. I was initially not pleased with the scores, but after looking at the old test 2 tests, some of the students made significant improvements. The one disturbing feature of responses I see is when students attempt to use a completely unrelated equation. For example - in the problem with the rotating Earth. I asked for the tangential speed given the angular speed of the Earth and the radius of the Earth. The appropriate solution is to use:
screenshot_02
Where omega needs to be in radians per time (second or minute or whatever).

Unfortunately many students seemed to focus on the word "tangential" and connected this to the aT, the tangential acceleration. In this case, the Earth is not changing its angular speed, so the tangential acceleration is zero. Another common equation used on this question was:
screenshot_03
This equation is valid, but finding the frequency will not help you answer the question.

WebAssign Grades

Note: Don't pay attention to the total grades webassign posts. In reality, the homework is worth 100,000 points and the tests are 175,000 points (this is not reflected in WebAssign). Also, the test 2, I posted as a percentage - not points.

Test 2 Grades

I have posted test 2 grades on WebAssign. The grades are listed as a percent (so it will be easier for you to evaluate your grade). If you want to know your score, simply multiply your grade*1.75E3 (that is 10^3 instead of 10^5 because your score is out of 100 instead of 1).

The grades were not good. Even the responses were poor, with many students either putting down nothing as a response or something incoherent. I suspect that part of the problem is that many of you waited until this week to look at homework, but it seems there were some of you that were working more consistently (and still did poorly on the test).

I am willing to give you a chance to show that you do understand the material. On Friday March 9, I will give an optional make-up test on the same material. I will keep the higher of your first test and the make-up test.

Equations for Test 2 (Again)

Yes, there was a small error on the equations I posted for test 2 (it was a typo error). The equations in the text are correct. I have fixed this error.

Chapter 4 Summary

This chapter focuses on motion that has a constant acceleration (except for the part on air resistance). Here are the key points to remember:
  • The kinematic equations (see the test 2 equation list) apply for cases with constant acceleration

  • Two dimensional motion is two sets of 1-D motion. If an object is moving in the x and y direction, you can use the kinematic equations for the x and y motions separately (with separate accelerations). The only thing these motions have connected is the time. The time it takes to complete the x-motion is the same as the time it takes to complete the y-motion.

Chapter 3 Part II Summary

The last two concepts in Chapter 3 (that were not on test 1) are Newton's second law and relative velocity.

Newton's Second Law:
Basically, this is the same as what we did in Chapter 2 except that the net force does not have to add up to zero, instead:
screenshot_08
This is a vector equation, so it is sometimes easier to write it as:
screenshot_09
screenshot_10
(note that this is essentially the same thing as the momentum principle)

So, what is different? The only difference between this and chapter 2 is that the acceleration may not be zero. Other than that, use the same strategy for equilibrium cases.

Relative Velocity
Here is the key equation:
screenshot_11
Where the subscript (vAC) means the velocity of object A with respect to object C and so forth. The key with this equation is that it is a VECTOR equation. You must add these velocities as vectors.

Test 2

I have posted the equations for Test 2.

VPython and Excel

Hopefully I will show you a numerical analysis in class on Friday. If you are interested in this, you can look at my PLAB 193 site where more instructions can be found. In particular, look at lab 3.

Problem Solving Worksheet

In order to assist your problem solving skills, I am posting a "problem solving worksheet". This worksheet will help you organize your solutions. The worksheet can be found in the resources section.

HomeWork and Test 1

Here is a graph of grades on test 1 vs. homework
screenshot_03
Hopefully, you will complete the homework. Notice the students inside the red circle. Those are all the students that scored higher than a 70% on the test. They also all scored greater than 80% on the homework. Does this mean that you MUST do your homework? No. Does this mean that if you do the homework, you WILL score high on the test? No. (some other students scored 90% on the homework, but lower than 50% on the test).

Test 1 Grade Distribution

Here is the grade distribution for Test 1
screenshot_11

Concepts for Test 1

For test 1, you should be able to do the first 5 homeworks on webassign and understand the following key ideas:


Chapter 1
You should be able to convert units. Really, that is the only thing other than dimensional analysis that was covered in chapter 1 (dimensional analysis is really the same thing as unit conversions). One other useful thing in chapter 1 is the problem solving guidelines (page 12). This is a general strategy to use when solving problems.

Chapter 2 - Force
The goal of this chapter is to look at forces. You should be familiar with the vector nature of forces. In terms of vectors, you should be able to:
  • Find the magnitude of a vector
  • Find the direction of a vector
  • Break a vector into components
  • Add vectors

You should be familiar with the following forces:
  • Gravity
  • Normal Force
  • Static and kinetic friction
  • Tension

You should also know that if an object is in equilibrium, the net force on that object must be zero. This can lead to all sorts of questions that involve solving for some unknown quantity. To solve these problems, use the following general strategy:
  • Indentify the forces acting on the object
  • Draw a free-body diagram
  • Choose coordinate axes
  • Set up Fnet-x = 0 and Fnet-y = 0
  • Solve for unknown quantities


Chapter 3 - Position, Velocity, Acceleration
You should know the definitions for average velocity and average acceleration (in vector form) and use these definitions in kinematics problems. You also need to be able to interpret position-time, velocity-time, and acceleration-time graphs.

You should also be able to determine position, displacement, velocity, acceleration and time for a problem with constant acceleration.

Chapter 7 - The Momentum Principle
The two key ideas you need from this chapter are
1) momentum
2) the momentum principle.

Here are the equations I will give you for test 1:
test1

Practice Test 1

Because I know you are going to ask for it anyway, here is an old test (not necessarily covering the same topics). WARNING: Do not try to memorize this test. First, I will use different questions and second that strategy does not work.

Overview so far

Here is what you should know so far.

Chapter 1
You should be able to convert units. Really, that is the only thing other than dimensional analysis that was covered in chapter 1 (dimensional analysis is really the same thing as unit conversions). One other useful thing in chapter 1 is the problem solving guidelines (page 12). This is a general strategy to use when solving problems.

Chapter 2 - Force
The goal of this chapter is to look at forces. You should be familiar with the vector nature of forces. In terms of vectors, you should be able to:
  • Find the magnitude of a vector
  • Find the direction of a vector
  • Break a vector into components
  • Add vectors

You should be familiar with the following forces:
  • Gravity
  • Normal Force
  • Static and kinetic friction
  • Tension

You should also know that if an object is in equilibrium, the net force on that object must be zero. This can lead to all sorts of questions that involve solving for some unknown quantity. To solve these problems, use the following general strategy:
  • Indentify the forces acting on the object
  • Draw a free-body diagram
  • Choose coordinate axes
  • Set up Fnet-x = 0 and Fnet-y = 0
  • Solve for unknown quantities


Chapter 3 - Position, Velocity, Acceleration
You should know the definitions for average velocity and average acceleration (in vector form) and use these definitions in kinematics problems. You also need to be able to interpret position-time, velocity-time, and acceleration-time graphs.

Physics Supplemental Books

I have had a couple of students ask about supplemental books for PHYS 191. I have two recommendations. The first is Introductory Physics with Calculus (as a Second Language) by Thomas Barrett. Although this is a book for the calculus physics course, there is still much useful info in it.

The second book is The Physics Toolbox: A Survival Guide for Introductory Physics by Hubbard and Katz.

There may be some other books that you could find useful, but I have looked at both of these and they seem to be worthwhile.

Physics Resources

I added some links on the physics resources page. On that page I will put links to software and applets that I believe you will find useful.

Homework for Test 1

I incorrectly stated that all the webassign homework for test 1 was up. Apparently, that was incorrect - but now I fixed it. There are 5 homework assignments covering material for test 1.

WebAssign for a Grade

Just a clarification about WebAssign being "optional" as stated in the syllabus. At the end of the semester, I will calculate your grade both with and without WebAssign. I will then use the higher of these two grades.

Math Test

You can pick up your answer sheets from the math test in class. It is clear that some students need some work in math. If your score was greater than 30 out of 35, then you seem to be ready. I would estimate a score of 20 out of 35 would indicate you could be ready, but there may be a couple of weak areas. If you scored lower than 20, I suggest extra math practice.

If you want to look at the test - there is an online version (that right now does not give feedback), but the questions are the same. Online math test

Resources for Math

WebAssign

A reminder about WebAssign. First, you can access WebAssign through blackboard or directly via http://www.webassign.net. You can obtain an access card either through the retail bookstore or directly from WebAssign.

I put a sheet with info about webassign here.