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.

Force / Vector Addition

Terrance Gibson also had some notes on the Force Vector Addition lab, which he found to be very good:

On the Force Vector Addition lab, the purpose of the experiment is to examine vector addition using a force table. The setup of the lab is fairly easy and simple. The directions for the lab are straightforward and not misleading. The only problem I have seen with the lab was that the strings for the weights are hard to tie to the rings if you have fairly large hands, and you can waste a lot of time doing that. I also observed that the force table needs to be on a level surface, I tried it in different locations and came up with different data depending on how level the table was. But all in all, this is a wonderful lab for teaching the students Force Vector Addition.

Impulse Momentum

Terrance Gibson had some notes on the impulse momentum lab to share. He's going to work on revising it for a bit better & more reproducible results.

On the Impulse Momentum lab you should analyze the change in momentum during a collision. However this lab is very hard to follow. It is not a one class period lab because the setup takes a long time - especially trying to decide how the accessory bracket and the motion sensor go together. The directions are very misleading, they don’t give a clear picture of how the setup of the lab is supposed to go. By the time you have set it up the, class period or block would be nearly over. There are also too many directions for a student to follow, which probably makes them bored with the lab, leading to bad results. So I feel the lab needs a lot of improvement and need to be shorten especially, so it can be accomplished successfully in a block or period. 

Work Thus Far...

As Dr. LeClair requested, here is a description of what I've been working on so far. After reading a few of the ASIM labs and learning what sort of equipment they had on hand, it was pointed out to me that the Archimedes' Principle lab was confusing and a bit long in its present state. After reading it, I agreed and did a rewrite of the lab, intended for use with the GLX. Here is a link to that rewrite (I believe it is the correct version) Archimedes' Principle Lab .

Problems I found with the old lab:
Directions were unclear at times, as were diagrams. The directions were also long, and yet not very step-by-step
It was not necessary to measure the volume of the rod used since it was being placed into a fluid in a graduated cylinder.


The lab writeup length hasn't changed, but hopefully the things in it are much clearer now. I'm currently working on a laptop + Data Studio version of the writeup, as well as teacher notes for the lab. I'll post them when I finish them. Also, any testing and feedback would be greatly appreciated.

Work -Energy Theorem

I believe Ryne is working on this lab. Here are some comments from the other specialists.



Getting reliable, repeatable results using the motion sensor will be close to impossible. For example, substituting the motion sensor for the photogate in the Conservation of Energy Lab will give errors that are much larger and erratic.

Tommy Morgan
ASIM Physics Specialist

Good morning everyone,



I present myself to you once more as the resident GLX ignoramus. But at least this time, it’s just questions, not problems. I recently checked the equipment (including GLX) for 8 lab stations for the Work-Energy lab. I wanted to make sure that all Force Sensors, Motion Sensors, and GLX would do their job correctly before dropping it off at a school.

Although the write-up cheerfully proclaims (Equip. Setup, #2) that the GLX will open to a Position-Time graph, all 8 opened to a Force-Position graph. Also, when I moved to different graphs (by changing the axis parameters) I found that “position” was the default measurement of the x-axis for all three graphs. I don’t know how to create or change a default setting. Of course, we can change it every time we move to a graph, but is that how it must be done? If you’re wondering, yes, I had Position-Position graphs instead of Position-Time graphs.

The lab talks about using the portion of the Force-Position graph that is horizontal (Analysis, #6), however every time I ran a test, the Force readings alternated about an average position which was just about right, judging from the mass hanging on the string. What little horizontal part there was, usually did not extend beyond about 4 data points (at the most). This was with 8 different Force Sensors and 8 different GLX. Also, the reading was only to a tenth of a Newton while I could make reasonable guesses to the hundredth of a Newton simply by looking at the position of the data points on the graph. In other words, the graph would bounce back and forth and the cursor readings would be 0.2 N and 0.3 N (alternating) although I could see that the real points were probably 0.24 N and 0.26 N. Is there a reason for this or is that just the way it is?

In regard to using only the horizontal part of the graph: If we only use a portion of the Force-Position graph, say from 0.3 m to 0.45 m, then the Work value we obtain will be the work between those points. Why would we not need to find the change in velocity between those points in order to calculate the change in kinetic energy that correlates to the amount of work done from 0.3 m to 0.45 m? Yet the change in kinetic energy found by the instructions in the lab is from start to finish (Analysis, #7) using the max. vel. found before being concerned about a horizontal part of the Force-Position graph. Should we use the Linear Fit tool on the Force-Position graph and then use the distance from start to max. vel. to get a work value that would correspond to the max. vel. we’re using (from Analysis, #3)? Apparently this has not caused problems in the past, so there is something here I am not understanding.

By changing the measurement parameters of the x-axis on the velocity graphs, I think an interesting question to challenge the students with presents itself. To wit, “Why is the graph of Velocity-Time a straight line, but the graph of Velocity-Position has a decreasing slope, like a root curve?” I was thinking it might be good, although a little tricky, not to mention the Velocity-Time graph and just ask why, if the acceleration is constant, does the Velocity-Position graph curve downward instead of being linear?” They might assume it should be linear, not realizing that applies to the Velocity-Time graph, not Velocity-Position. Then they have to start thinking to make sense of it. I know this is not the purpose of the lab, but understanding what the graphs are saying is part of the COS.

I welcome any help with any of the above, and thank you.



Jeff Woods

Interference (Sound)

I'm trying to write a lab using the portable speakers in the storage room. Right now I'm including interference due to two sounds of the same frequency in different phases, beating due to two different frequencies, and determining the wavelength by measuring the distance between successive destructions.

Can anyone think of anything major that can be included in the lab that isn't already?

Demonstrations

How do we feel about trying to come up with demonstrations for some of the more esoteric stuff (charge interaction, magnetism, etc.) that the students are otherwise probably only going to see in a Physlet?

Welcome!

This is where we will keep a log of our efforts to help improve Alabama Science in Motion physics experiments. This effort is part of PH405, Physics for Science teachers, during the Spring 2010 semester.

We're working on both streamlining existing procedures and creating new ones with the wealth of existing equipment.