Skateboard Acceleration

I ask for a smaller (less massive) student to volunteer to be pulled on a skateboard, while the rest of the class measures and records data. We mark out a straight path in the cafeteria (it has a smooth floor) with marks at 0, 5, 10 and 15 meters.
Students are assigned to work in two teams each at the 5, 10 and 15 meter marks, two students with timers (stopwatches) act as spotters. The spotters are to record the elapsed time from the start signal to when the nose of the skateboard crosses the mark. The second student acts as a recorder, to collect the data.
I use a 20 newton spring scale to measure the force that I apply to the student. I try to keep that force at 10N while running backwards (practice this before hand!) I also measure, ahead of time, the amount of force needed to pull the student at a constant velocity- this gives me the kinetic frictional force on the student, which must be subtracted from the applied 10N force.
When all teams are ready, and we have practiced, I call out a countdown and start running backwards. It is best to place your foot against the nose of the skateboard and hold it in place before you star, so that you can apply the full 10N force right from the beginning. As I pass each team, the stop their timers and record the data.
We repeat the experiment 5 times, and then return to the classroom.
I then have the student call out their data, which re write on the board. Then all students transfer the data to a data table, and start their analysis. The average the times, calculate the velocity and acceleration that occurred, and graph the results. V=at, d=1/2at^2 are the only equations needed. We check to see if the acceleration was equal at each mark point.
We then use Newton's second law (F=ma) to check our results. We rewrite the equation to solve for m, and then check to see if the mass that we have calculated is close to the mass of student + skateboard. We are always within 10%, and often closer.
The students learn through visual and tactile clues the relationship between mass, force and acceleration. They easily see the difference between velocity and acceleration. They get practice in calculation and graphing. They have to work together as a team to get all of the data. They also have a lot of fun while doing it.
Students have to complete a full lab write up on this assignment, including a hypothesis, procedure, data table, analysis and conclusion. Error analysis can be added as an extension.
We could add a video component to this, and create a video graph of it using Vernier software if we had the cameras!