GS 104 Lab Report: Slickness Factor
I) Freebody Diagram (Force Picture): Because we are going to be exploring a system where the directions of the forces acting on an object may not be so obvious it is important that we start by clearly illustrating the forces we think are acting on the object and in which directions. The object you will be examining is a lab mass as it slides down an inclined surface.
The experiment itself is fairly simple. Place the lab mass (start with the 200g) on the incline and elevate the incline until the mass starts to slide down the surface. Eventually you will be trying to adjust the steepness of the incline so that the mass slides with constant velocity. At the same time you are gaining some experience working with forces you will also be observing some potentially unexpected behavior of friction between rigid objects.
As you approach the task of doing the freebody diagram consider the non-contact and contact forces which might be acting on the mass. For each force you put on your drawing list the two partners which "produce" the force. Also indicate the object on which the 3rd law partner to the force you have drawn acts. (If you ignore air resistance you will probably find 3 forces)
II) Data: In this case your data will consist of the mass of the object sliding down the incline, a measure of the steepness of the incline, and a note about the specific surfaces which are rubbing together to produce the friction. Repeat the experiment described with each of the three lab masses you have been given. Repeat the experiment with each mass until you are confident that you have determined the steepness or slope of the incline for which the mass slides with constant velocity. Measure the slope by determining the rise and the run of the incline piece of paper towel underneath the lab masses.
III) Analysis:
1) Which of the forces on your freebody diagram is responsible for moving the lab mass down the incline? Is the effect of this force the same regardless of the slope of the incline? How can the effect be different for different slopes if the force on a particular mass doesn't change?
2) If the masses are sliding down the incline at a constant speed what do Newton's Laws have to say about the balance between the force(s) dragging the mass down the ramp and the force of friction?
3) Does this mean the force of friction on each lab mass is the same or changing? Explain your reasoning.
4) What do you deduce from this experiment about the relationship between the slickness of the surfaces and the slope of the incline? In fact, we could define a slickness factor (SF) which is the numerical value of the slope of the incline. Calculate this SF for each of the two experimental settings. In more formal terms this number is called the coefficient of kinetic friction but we'll just refer to it as the slickness factor (SF) :)