# 121 Winter 2019 Week 2

Monday

Before Class
– I posted the lecture slides from Thursday’s class by the “during class” part of Thursday’s timeline, Week 1.
– What if you want to see a video the second time and also want to see the questions? Just click on the small vertical bars at the bottom of the video that indicate where the questions are located in the video.

1. The course grader made the first video inspection Thursday morning. So, if you added the course late or for some other reason, did not watch videos until Thursday morning, you still received full credit.
2. Finish PS#1
3. Our preparation Thursday took more than the time than I allotted so there was little time for Big Exam! #1, but I thought the time was well spent. Let’s make the best of it. Please hand in Big Exam! #1 today in the form that you think is exactly what is worth full credit. I will correct this BE#1 and get it back to you Tomorrow (Tuesday) so you have a good idea of what I expect for a midterm. Feel free to work in groups.
4. View Pushing Box Problem.
5. Do this short survey #1 – it counts as a video. Please consider your lens all the time.
6. View this 3 minute video : Energy, Work, and Power. Be prepared to answer this question: a 1000 kg car starts from rest and accelerates to 30 m/s in 5 seconds. Please calculate the average power the car produces to do this. Please put answer in Watts and Horsepower.
• 2.0 Forces and Work
• 2.1 Power
• 2.2 Units

During Class
– Prepare for our activity/project #1 we will do Wednesday: You will make a video and calculate the kinematics, energy, momentum to be handed in next Tuesday.
– Hand in PS #1 (corrected by grader)
– Hand in BE #1 (corrected by me)

After Class

Tuesday:
We are going to graph some of our own motion, forces, energy, and power tomorrow. In today’s videos, you will see several ways to extract kinematic data from a video. The full description of the project can be found on a link from the main class website.

Before Class:

1. Please view the video kinematic graphs, LIVE! and watch me draw graphs on a board to represent my motion on a bicycle.
2. View Smarter Every Day Grasshoppers, and try to repeat his experiment with the other grasshopper. You can download Tracker at this website. You may have an easy time doing this, or you may have great difficulty because of software compatibility. A past student wrote this to help: Tracker Video Instructions. Please work together. In the face of fighting with malicious software, you need good friends. All the same, if it doesn’t work for you, don’t sweat it, but please try to estimate the acceleration some other way, like using my Excel method in the graphing video I did below. One student was able to get tracker to work on a Mac only after transforming the video into a .mov… here it is Grasshopper .mov
3. You can download Tracker from this website and use it! This is great for us because it means we don’t need to use university computers. Please try to do it yourself on your computers before tomorrow.
4. Work on PS #2
5. You will likely use Logger Pro (or Tracker) to analyze your motion data, so please see how we can collect our kinematic data using Logger Pro.
6. Please see how we can analyze our kinematic information from Logger Pro using Excel.
7. Tomorrow, Wednesday, we’re going to meet at Via Carta to take videos of us to calculate kinematics, forces, energy, power, and look at momentum conservation. The first project description link is on the main class webpage. Please take a look at it. You can actually do this analysis without any software (Logger Pro or Tracker), which I show you in the videos for tomorrow. You can look at them today if you want.
8. Readings: 2.3 Graphical Analysis of Kinematics
9. Read the description to project #1 on the main class website.
10. A number of students asked yesterday about the “finding the power output of the car” problem, “which speed do we use to find the power output?” There’s a number of ways to answer this question. The answer depends on which lens you use. Try “Power is the rate of change of energy.” You know the time and you can find the kinetic energy. Which speed will you use for finding the final kinetic energy?

During Class
Practice and prepare for activity tomorrow.

Wednesday: Meet at Via Carta Today Tomorrow Next Tuesday!

Office hours have been switched Wednesday to 2:00 PM
we will analyze data on our movement.

Before Class

1. Solutions for Big Exam! #1 posted on main class website.
2. I graphed my motion without Tracker. Please view: Graphing running
3. Graphing a ball toss.
4. Please see how I solved the
5. See a video about how to measure power
6. Have you ever played the “rope pulling on a stump” game? Why can’t you just pull the other person off the stump? What happens to you if you pull really hard? Which lens are you using?

During Class:

Thursday: Vectors in the four lenses, proving energy formulas.

The vector sum of the Forces = mass * acceleration.

We will explore more complicated dynamics problems.

Before Class

During Class

• Big Exam! #2
• So ends two weeks of 141. How is your experience so far?