Physics

Here is the second video. (Click to go to YouTube.) If you thought the last one was funny, then you’re going to love this one. This one is also shorter at a little over 6 minutes.

If you want to print the slides for your notes, they are here.

“Chugga chugga choo choo! Time’s up!”

I made a short video, as promised, which you can see here. Someone pointed out to me that I stapled a couple pages in the wrong order in the packet, so the video also explains the correct ordering of the pages. Still have questions? Email me.

The packet is due on the first day of class, though I would prefer to hear from you before the end of summer with your answers to the survey questions.

The University of Colorado has lots and lots and lots of those simulators. Enjoy.

(If there’s a concept you aren’t understanding, playing around here might help. You never know.)

I use these Concept Tests in my regular physics class. They’re good for strengthening your conceptual understanding of physics.

Only five people in class today. Wow. I hope everyone did well at their various competitions. Luckily we have three full blocks next week. One of those blocks will probably be a quiz.

• Today we finished Chapter 10 by talking about elastic potential energy. Those problems that I assigned way back when will be due on Monday.
• After finishing Chapter 10 we went right into Chapter 11 – Fluids. I made a couple hand-outs for you to look at… the brand new Chapter 11 Toolbox and a Chapter 11 Summary. Both are pdfs.
• I assigned some Chapter 11 homework which will be due on Monday as well: p.353 (7, 15, 18, 21, 33, 35, 40, 43, 59, 67)
• Monday will be a big homework review day.

For fun, you can read these Fermi Questions. (Note: this type of problem is named for Enrico Fermi.)

Email me if you need to.

When you’re trying to determine the velocity required to negotiate the loop, consider this diagram:

At the topmost point in the loop the centripetal force is provided by both the force of gravity (mg) and the normal force (Fn). If the marble loses contact with the ramp, Fn = 0; there must be contact between the ramp and marble for a normal force to exist. So by setting the normal force to zero you can look at that point when the marble just leaves the ramp’s surface.

If you have other questions leave a comment. First names only please.

The web has a super-charged version of the TI-89’s “solve” function. It’s called Sage, and it’s an open-source version of mathematical modeling programs such as Mathematica and Matlab.

Go to the Sage website and click go to “Sage Via the Web.” (The Milnix.org link seemed to work better for me.) Create an account for yourself and try it out.

The code required to solve our Atwood Machine Problem is:

a1, a2, a3, T1, T2, g, m1, m2, m3 = var(’a1 a2 a3 T1 T2 g m1 m2 m3′)
eq1 = a1 == -a2 – 2*a3
eq2 = T2 == 2*T1
eq3 = T1 – m1*g == m1*a1
eq4 = T1 – m2*g == m2*a2
eq5 = T2 – m3*g == m3*a3
solve([eq1,eq2,eq3,eq4,eq5],a1,a2,a3,T1,T2)

The first line of code defines all the variables we worked with. You must do that or Sage gets confused. The next five lines define our five equations. The last line is you favorite, which tells Sage to use the five equations to solve for a1, a2, a3, T1, and T2. Four pages of algebra or seven lines of code. Which would you rather do?

Can you always use Sage? No, because you need to be able to handle the algebra without a computer on the AP exam. Though there’s probably no way they will give you a problem that’s this involved.

If you want to use Sage to help you solve equations, it’s probably best to ask me first or just use it as a way to check your work.