Archive for December 2010
Am I the only teacher that spent half of the holiday break grading papers and working on lessons? Here is a lab my students will be working on when they come back from break on Monday. I figure it will give me a day or two to settle in without having to get up front and teach.
We just finished Newton’s Laws before break, what better way to refresh their memory than making them think. I got this lab from the NSTA regional conference in Baltimore, it is called “Inquiry in a Box” and presented by Deborah Roudebush. I put the instructions into a format my students are more familiar with and I expect they will need two days to get their arms around the whole thing. What is very different about this lab (compliments to Deborah) is that the students are given only the problem to solve, some minimal tools, and no instructions. They need to figure it all out on their own. It could be a disaster, I fully expect a lot of whining.
The basic idea is that the half ball Party Popper shown above is a cool little science experiment. Giving them only a ruler and access to a gram scale, they need to figure out how to determine the velocity, time, and force exerted by the popping event. At the conference, we were put into groups of four and set about solving the problems. It didn’t take us too long, but there were some very good discussions on when the time and acceleration actually occurs. There will be no answers posted here, some of my students know about this site. If you need some help, email me.
Here is the lab handout: Popper Lab Handout
Now, you would think these little poppers are easy to come by… good luck! I went to many toy stores and party stores and found none. I ended up online at Oriental Trading Company. Their 1.5″ poppers are great, their 0.75″ are going back, they don’t work at all. I found another place selling them; Century Novelty. I’m ordering 1″ poppers from them. The key here is you have to plan ahead for this lab, you can’t run out to the store the day before and find them easily. I won’t have the 1″ poppers in time for this year, but next year I plan for them to analyze different size poppers and compare the results.
This is a follow up on the first pass of a lab I created about a year ago. You can see my first post here. This year we purchased a whole pile of new technology including the LabQuest from Vernier. If you have these in your lab, you know just how cool they are. The kids love technology, this lab grabbed their interest.
When I came up with a lab last year, we used spring scales to attempt to measure the coefficients of friction on all different surfaces. Let’s face it, doing this with a spring scale was mostly guesswork. I enhanced the lab with the digital force meter, made a few quick modifications to the instructions and gave it to the kids. The results blew me away.
The graph you see below was printed directly from the LabQuest. I tried exporting it as a file, but the export file wasn’t an image file, so I scanned it for all of you to see. Click on it to see it full size. The red line shows the force required to pull a painted steel plate across linoleum. You can clearly see the spike where the pulling force overcomes static frictional force. The next horizontal data set shows that the object was pulled at a constant speed. We can read both the static and kinetic forces directly on the LabQuest.
I included a shrunken image of this graph on today’s test. I gave the students the weight of an object and they had to calculate the two coefficients of friction from the graph.
Here is the handout: Measuring the Coefficient of Friction – LabQuest, feel free to steal it and use it. If you have ideas to improve it, leave me a comment.
Here is an interesting finding – shoe rubber seems to have a static coefficient that is the same as the kinetic coefficient, pretty much regardless of the surface. On linoleum, it’s around 0.60.
I was discussing Newton’s Laws and trying to explain how the tension increases in an elevator cable when it starts moving up. The kids get it that the tension when it’s not moving is equal to the weight of the load, but once it starts moving, they get wacky. Some seem to think the only weight at that point is the force from F=ma and the elevator is now weightless.
I put 1 kg mass on the large spring scale and showed how it pins the reading if I pull up. They saw it, but it didn’t click.
On a whim a took I put the 1 kg mass and lifted it with some string. My standard classroom string is macrame string from A. C. Moore. It costs about $3 for 1000 ft ball of string. I think I go through a ball of it every year. Anyway, the 10 N weight is nearing the limit of what the string can hold. I accelerated the string upward just like I did with the scale and the string snapped. Watch your toes, it fell to the floor and cracked a tile… oops.