Thoughts on studio physics?

This is an open thread to collect comments, suggestions, and observations on studio physics at UA by our LAs and TAs. If you are a current LA or TA, email me and I can make you an author if you would like to create your own posts.

In your comments, please note whether you are a GTA or LA, and whether you are a US or international student. This will keep you anonymous, but give us some context for your comments.

Friction Lab

Chris and I have been working on a new way to measure the coefficient of kinetic friction. Our writeup can be found here. We got very consistent results with this method, so it should be better than the old lab by a good margin. Any comments or testing would be welcome.

Work-energy

Ryne Saxe has heavily revised the Work-Energy lab, with great results. He's re-written the writeup, and come up with some teachers notes as well. His work can be found here.

Plane & Curved Mirrors

Terrance Gibson ran the plane & curved mirrors lab, and found it to be in good order. Some comments:

The reflection – plane and curved mirrors is an experiment to better understand how rays are reflected by determining the focal length and radius of curvature of different types of mirrors. The setup of the experiment is very straightforward meaning easily to follow and not much equipment to use at all. However I prefer doing the experiment in a dark room to see the light rays better. I think if you try doing this lab with different color paper instead of white paper it might work better, you might not have to turn the lights off. But, all in all, this is a wonderful lab to continue doing to understand how rays are reflected, using a protractor, and ruler to obtain the angles of the rays.

Friction lab (kinetic)

Eric, Chris and I may have hit on a way to do the friction lab with reproducible results -- it worked pretty well today with a variety of different sliding objects. The basic idea was to slide a block on a flat track and let it go, and use the ultrasonic position sensor to measure its velocity decreasing with time after you let go. The slope of v(t) should give you (mu)*g. We tried it with aluminum and wood blocks today of various sizes, and it was fairly reproducible. If we continue to have good luck, it might be a good alternative to the varying the angle of an inclined plane -- kinetic friction seems more reliable than static, and doing a slope measurement averages out a lot of the uncertainty. We'll see if it continues to give reliable results ...

One objection might be that we are measuring kinetic instead of static friction, but myself I don't see this as a big problem. 

Simple harmonic motion

Ryne Saxe has heavily revised the simple harmonic motion lab and written up some teacher's notes. You can find our current version of both here (Word documents).

Conservation of Energy

I enjoyed this experiment. If done correctly it produces very consistent data. There are a couple of things that are key when making sure this experiment is done properly.

I know previously this experiment was conducted by lifting the track with books, but after running through it a couple times I noticed that this produced some inconsistent data. Instead, I used the stand which made the track stable and gave me better data.

It is also very important to make sure that your picket fence is lined up perfectly with the photogate. If it isn't you will collect data on some runs and not on others. The best way to make sure it is aligned is to do a slow test run. Place the fence on the cart and try to line it up so the 13 bands block the photogate beam. Then slowly drive the cart through the photogate. The red light on the photogate should flash as each band blocks the beam.

Lastly, it is very important to make sure you start your cart from the exact same place each test run. This ensures that the distance doesn't create a hiccup in your data.