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Always under the conditions of the tests! Clean dry surfaces, etc.
If I read the above paragraph correctly, am I to conclude that slipping
friction (kinetic) is always greater than static friction? Balderdash.
I look forward to playing with this. Our poor physics program didn't have the
I have my students pull different masses across a table surface with a
calibrated force probe. The students will pull the mass at a speed as
constant as possible, then stop, and pull again. There are definite
spikes (static friction) and the kinetic friction (sliding) is much
lower. If the blocks are allowed to rest on the table for a period of
time, the first spike is much higher so we just average the spikes after
the first one. They are all nearly the same. There is a direct
relationship between the pulling force and the mass of the blocks.
We wrap the blocks with paper to provide the same surface. The bottom
block is turned on edge to provide a smaller surface area. Within the
limits of uncertainty, the force is independent of the surface area but
the results are less than convincing for most students.