Sledding and Sliding on Different Surfaces: Experiences with Friction
Posted by: Peter Rillero in High School Science, Middle School Science, On-Line Learning, physics, Science Activities, science education, science instruction, Software Reviews, tags: friction, momentum, snow
Living just north of Phoenix, we get the warm sunny 70° January weather, but we can drive 100 miles to the north to play in snow. Snow takes on a reverent beauty when you are just visiting it, playing in it, and having the air full of thick, downy flakes. When it makes unwanted intrusions, such as when I lived in New York, Ohio, and Iceland, it becomes more difficult to appreciate.
To the right you will see some snow fun pictures from our snow play in Flagstaff yesterday. It is interesting to see the evolution of “sledding”. Even in my childhood, toboggans were on their way out. Wooden sleds with two rails and a steering bar, like the Flexible Flyer, ruled the hills. I didn’t even see one of these on the hills. The disc or flying saucer seems to be waning. The flexible-foam, body length “sled” is the new king of the slopes. But what slides down the snow best?
The “coefficient of friction” (COF) is used to express the amount of friction between surfaces and this is proportional to the force pushing the surfaces together, or the weight of the rider and sled on the snow. The greater the COF the more friction there is. The COF for not-yet moving surfaces (static friction) is greater than sliding surfaces (kinetic friction). Engineers have measured different COFs (link). For instance, the kinetic COF for leather on oak is 0.52 and for those interested in glass-on-glass action, the kinetic COF is 0.4. Google has enlightened me. I had no idea there was so much research done on snow, and that there is a vibrant field called “snow engineering”, which might be called the ultimate snow job. Without going too deep into it, the COF for a moving skier (ski on snow) was analyzed to be between 0.01 and 0.3. I’d have to think that metal on snow would be a lower COF than foam on snow. It is good to think about, and students could do some fun experiments to find out.
Virtual science experiences must engage students and must have rich interactions. If it is just a Flash animation, I am not ready to call it an “experience” when the term video is much more suitable. If a teacher is going to bring laptop carts into a room or sign up weeks ahead for the computer lab, they should have computer-learning experiences that feature an engagement, a significant interaction, a closure, and multiple means of assessment.
“Sliding on Different Surfaces,” an Activity Object by Adaptive Curriculum, features these aforementioned characteristics. For an engagement, students play a game where they steer a sled down a hill while encountering different types of surfaces. If they steer over the surfaces with the least amount of friction, they will go faster. They receive a score based upon how well they did.
In the student interaction, students are in an office. They slide a pencil case across a desk and then mark the distance. Their mission is to find different things in the room such as a towel, newspaper, and sandpaper (obviously a rough office) and see how the pencil case sliding distance varies. (Elearning Physics Preview)
This elearning physics experience moves forward to an explanation of friction and factors that influence friction. There is an optional paper-and-pencil activity sheet that students can complete as they do the Activity Object, with two questions to be answered when they are finished. The activity sheets promote writing and become a permanent record of their learning for their science notebooks. If a teacher has a projector or interactive whiteboard and is doing a whole class lesson, the activity sheet is even more essential.
After the closure, students move onto the multiple-choice assessment, where they answer five questions and receive instant feedback about their learning. Teachers can log in to access student scores for the assessment. They can also see how long students took doing the Activity Object. If students are up for a bit of gaming, with their new understanding of friction, they can go back to the game and improve their time.
I did the Activity Object and played the game, and I observed that compared to my 8 and 11 year old sons, my sled in Flagstaff went much farther than their sleds. I would like to think that this was because I selected the patches of snow with the least friction and thus I picked up more speed. But these foam “sleds” are not very steerable and so, unfortunately, I have to consider the competing hypothesis that since my mass is a wee bit more than my sons (well okay, actually my weight is about 50 pounds more than both of them together), this may have had an influence. Since momentum is equal to mass x velocity, my momentum should be much greater than my sons’, and thus it would take longer to bring me to a stop. An impulse (force x time) can change the momentum of an object. Since my momentum is much bigger, and assuming that friction is about the same, I coast longer and thus farther.
But I think I will choose the happier hypothesis – that my greater knowledge of fric
tion, rather than greater weight, made me go farther. Which just goes to show the subjective side of science after a happy family day in the snow.
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You say, “If a teacher is going to bring laptop carts into a room or sign up weeks ahead for the computer lab, they should have computer-learning experiences that feature an engagement, a significant interaction, a closure, and multiple means of assessment. ” I agree.
Basically, you must make the time valuable to learning science. In this particular example, you might have arranged to have old-fashioned in-class, hands-on experiments. The hands-on alternative is not always available for reasons of time, safety, space, and money. As nice as the Adaptive Curriculum object is, it misses one essential ingredient for science investigation: reality. You and the students know that the objects (towel, newspaper, sandpaper) are not real. They are only representations that may not truly mimic what you’d see if you did the experiments for real. Your data will be too perfect as well. Doing real-world experiments gives you data with noticeable random error and often somewhat ambiguous results.
Having perfect data gives students the impression that science functions in a perfect world. Student science investigations (aka “labs”) should always take students into reality rather than away from it.
There’s no technological barrier to providing the same capabilities as you see in Adaptive Curriculum but with real experiments in place of phony ones. Experiments could be prerecorded with many, many variations. Students could even take data point by point from the moving object to get the distance-time graph of motion and learn more than just how far the object moves or how much time it takes.
Huge amounts of money are being spent creating phony experiments like those in Adaptive Curriculum. Resources would be better spent on building real-world investigations. If you’re going to the trouble of using computers in a classroom, you should have the best possible science experience, and that experience should always include learning more about the nature of science, improving scientific reasoning skills, and understanding the complexity and ambiguity of empirical work.
Take a look at http://www.smartscience.net/howtouse to see one way to use prerecorded real experiments.