Measure the kinetic and static coefficients
of friction, then use the kinetic friction coefficient to predict the
acceleration of a block being pulled along a horizontal surface, and up an
inclined plane.
Method #1 for measuring friction
coefficients:
Draw a FBD, and find the smallest angle needed for an
object to slide down an inclined plane (static coefficient) and smallest angle for an object to continue sliding down the plane once started (kinetic friction coefficient).
Static coefficient – angle block starts
sliding at without being pushed
to get it started.
Kinetic
coefficient – angle block starts sliding at with
a push to get it started. (The kinetic
angle should be slightly smaller than the static angle.)
Discuss how to best take a tight turn!
Change the position of the pulley to create problem 12.72. Experiment with different weights for A and B until you get a mass ratio that produces a nice, slow, measurable acceleration. Record your weights, and friction coefficient. Predict, and then measure the accelerations of blocks A and B that are produced.
Example Pulley Problem: 12.3
(This is not exactly the same as your lab, but is similar, and should give you a good idea on how to do your lab calculations)
Data from Lab-Pro (if we can get it working!)
Read description of how it works here:
Example data set (that can be imported into excel):
Unfortunately, the velocity and acceleration data have issues due to error propagation, so we will need to clean up the data and create our own velocity and acceleration graphs in excel.
(Remember the error propagation issues from 1201 ? - see
We will need to isolate the data of interest (data when the block is moving)
Then, fit a 2nd order polynomial to the position data (just isolate the data you need, right click on the data, say "add trend line", select 2nd order polynomial, and show equation).
Take the time derivatives of your equation to find velocity and acceleration. (See graphs above, and equations below).
