054 Force of friction on a moving Ripstik

In passing during laboratory five I mentioned that perhaps the force of friction acting to slow the RipStik might be measured by dragging me along the sidewalk. Then I realized that this could actually be done. 

With a little more thought I realized that I could use F = Δp ÷ Δt to obtain a second estimate of the force of friction. As outline on the board, a three meter speed trap would obtain v₀. The kilogram spring scale in the prep room provided the mass m. Thus momentum p₀ was within each reach. Coasting to a stop influenced only by frictional forces would complete the calculation: (p₀ - 0)/Δt. 

This would require only two times: the 3 meter speed trap tranversal time and the total time to decelerate (which included the speed trap time)

Preliminary calculations suggested a force of 10 Newtons, which meant the brown 10 Newton spring scale might be sufficient. Choosing the brown spring scale proved to be an optimal choice as actual forces were less than projected.

Picture credit to Sheral. Shawn Dee is towing me while Mirabella was to have read the spring scale. She couldn't and my angle was not ideal for reading the spring scale either. Sheral would walk the second run and that would yield measurements of 5.25 to 5.5 Newtons. As earlier in the week, this is well within an order of magnitude of the force implied by the loss of momentum. This went better than expected. The stopping points were around 18 meters pre-class and 21 meters in class. Any more velocity and the board might continue on to the next down slope, which would invalidate the results. 

This activity wraps up Newtonian dynamics for the class. On the board I closed by listing velocity, acceleration, momentum, kinetic energy, and force.