Students collected data for the lab challenge. We have several ramps of different steepness near my classroom. The roadrunner is played by a constant speed buggy. The boulder is played by a cart. The tripwire is really just a blue piece of tape. When the roadrunner crosses over the tape, the group releases their cart. During today’s data collection phase, the students do not know where the tripwire will be placed. Their job is to model the motion of the cart so that, when they find out where the tripwire will be, they can use their model to predict how far up the ramp to release the cart.
Here’s a nice clip to introduce the activity:
Last week, students used motion detectors to test if the area of a velocity-time graph was equal to displacement for a variety of scenarios. However, Logger Pro did all the mathematical work for them. Today, students are using the graphs given by the Super Ultimate Graphing Challenge Game to calculate slopes and areas on their own. Then, they use the game to check their work. If they find that the area they calculated and the displacement shown in the game don’t match, they need to double check their work and then ask for help. I really like the self-checking nature of the activity. You can download a copy here: CA SuperUltimateGraphGame Displacement VT Graphs 2016 (PDF)
Students used motion detectors to test this out for a variety of scenarios. First they did it with a constant speed buggy to verify experimentally what we had already established during the Constant Velocity unit. Then they looked at new scenarios where the velocity was changing:
- A cart rolling down hill.
- A tissue box that speeds up (due to a push) then slows down (due to friction).
- A cart that moves across the table, hits a rubber band barrier, and returns back.
The moon stops moving and begins falling towards Earth. Determine….
- Work done by Earth’s gravity
- Moon’s change in kinetic energy
- Moon’s speed when it hits Earth
After realizing that the force wasn’t constant, we decided we could split the distance between the Earth and Moon into chunks and estimate the work done for each chunk. I lead the class through a quick-and-dirty GlowScript program that could do this for us. I prettied it up to share with you here:
(It’s an interactive Trinket! Change value of N to see how the estimated values for work and impact speed change.)
I need to improve how I incorporate these programming “lead-throughs” in class. I’m thinking maybe a sheet with prompts along the way. They wouldn’t be writing the program from scratch, but the prompts would ask them for key lines of code that I would add to the program I was writing. (I’m always torn between the time needed for them to code on their own vs. the time I can do it more efficiently as a demonstration to illustrate a concept.)
And now thinking about it, it isn’t really the code syntax that’s important, but how to break down the problem into the steps of what we want the code to do for us (split distance into chunks, calculate Fg at a chunk, calculate dW at a chunk, add up the dWs, etc.). So now I think a sheet with question prompts for code is counterproductive. Maybe have them write pseudocode on whiteboards which outline the general process instead?
(Sorry for the stream of conciousness rambling.)
AP Physics C students designed a lab to test if the work done by the rubber band on the cart was equal to the resulting kinetic energy change of the cart. Since the force of the rubber band on the cart isn’t constant, the group in the picture is collecting force vs. displacement data for the rubber band so they can graph it and find the area under the graph (work). The rubber band launched the cart towards a motion detector in order to determine the resulting kinetic energy of the cart.