Spring 17 Mechanics Week 3

For Monday: Vectors in the four lenses, proving energy formulas.

Before Class

Tuesday : Springs and Review
Before Class

During Class

  • Midterm #1 is NEXT WEEK Tuesday. We will not be allowed to discuss questions during the Midterms and final as we do during Big Exams. If you hand in formula sheet stapled to your big exam #2, I’ll check your formula sheet and make sure that everything is correct and relevant. Make sure it reflects your understanding.


Before Class

  • Solutions for PS #2 posted
  • See: Elastic Collisions with Walter Lewin at MIT
  • Then before seeing my video below, please read this very short statement about 2.9 changing references frames. Do the exercise.
  • Elastic Collisions with Pete at Cal Poly by Changing Reference Frames This is my most popular video – after ~ 4 years, it has over 18,000 views. See if you can tell me why it’s the most popular of my videos.
  • Read 8.4 from the original OpenStax textbook to see how the rest of the world looks at elastic collisions in 1-Dimension. Please reflect on the following two questions
    • How do you compare this chapter to the chapters that I write?
    • How do you compare this method to the picture drawing method that I present in the video?
  • Important to consider for today’s class… your life may depend on it. You have two balls to throw against a door in order to close the door with the impact of the ball. One ball is perfectly elastic, and the other one is perfectly inelastic. Which ball will be most effective at closing the door? Why?
  • Optional reading on NPR about active learning in Physics Education Research. The author, Carl Weiman who won the Nobel Prize in Physics for Bose Einstein Condensation gave a talk at Cal Poly some 12 years ago calling on us to evaluate and innovate teaching with the same scientific process we use for other scientific research. Since then, he’s become prominent in Physics Education Research. He’s published a considerable amount about active learning strategies and over the years has become more outspoken about the futility of the lecture model and need to change.
  • Another NPR article about education:
    • “The first step is to teach Socratically, by asking questions and having students think out loud. This works much better than lecturing.”
    • “Teachers who find their kids’ ideas fascinating are just better teachers than teachers who find the subject matter fascinating,”

During Class

Elastic Collisions

Surviving a fire in your door room


Goals: Learn about Friction

  • Dynamics: Friction is a force = to the product of the coefficient of friction and the normal force between two bodies.
  • Dynamics and momentum: Friction acts in the opposite direction of the relative motion of the two bodies exchanging momentum. So say, you are spinning your car’s tires when the light turns green. The tires are moving backwards relative to the ground. This pushes the tires forward and the ground backwards. You can see this especially when some of the road gravel flies backwards.
  • Energy: Friction turns kinetic energy or mechanical work into heat energy. In the above example, the tires and road get hot. In drag racing, the cars melt some rubber down on the starting pad by spinning their tires.

Before Class

  • PS #2 solutions posted.
  • Finish Video Project
  • Read 5.1 friction from the original OpenStax textbook. Please reflect on how this works for you compared to the short chapters I write like: 3.0 friction. If you want to know more about the molecular nature of friction and biomedical consequences, please see this OpenStax description.
  • Check out the video I made for you guys about dragsters and friction.
  • Prepare for midterm by doing last quarter’s midterm exam or midterms from other previous classes, accessible from the general sharedcurriculum website. Bring in your answers, questions, etc. Your midterm will be similar to this with the following difference. There may be some questions on your midterm that do not have a numerical answer. For instance, I might ask you to just set up a problem or consider a situation without calculating a numerical result.
  • Please see this video on using calculus to look at kinematics
  • graphing the motion, force, energy, power of an object: motion of an object, We didn’t do this problem on our problem set, but a similar problem could be on the midterm, so please watch it, and try to do it before I explain it… and come with questions if you have difficulty.
  • Review how I solve the Ballistics Pendulum Video from an old problem set.
  • Optional: another education article on NPR: How you think with your hand, not your brain (or at least not your computer).

During Class

How fast can you throw a ball?
Hand in your video project!

Midterm Preparation???

Hey, I wish I could look at even more midterms!… Hey take a look here: Fall 2017 MT#1, MT#1_W16, You can see answers, solutions and comments, if you go to the course website for these past classes.

If you want to make maximum benefit from this resource, you will NOT start by looking at the solutions. My recommendation is that you:

1) sit down and “take” last quarter’s MT#1 in 50 minutes under a test like situation, quietly alone.

2) “grade” your midterm with the answers and make corrections without the solutions. I recommend you do this with a group of students and feel free to check videos and/or your textbok to get more information. I bet it will be fun to do during office hours on Monday! allow up to two hours for this without looking at the solutions

3) Only after you have worked out the answers on your own, consider the solutions… the solutions are only the way that I did them, so make sure you recognize the value in the way you worked the problems too

This weekend

What are you doing to celebrate our planet on Earth day?, This Saturday?

Earth Day April 22nd at El Chorro Regional Park.jpg