Friction is a very complicated subject, but most elementary physics books
have a fairly good explanation. So in an effort to make some of the
effective labs available even when the necessary equipment is not available,
I have been creating fairly realistic simulations.
As usual I try to make the simulations general enough that they can be used
the same as actual experiments. So I have a cart on a ramp which is given
an initial push and then is sometimes caught at the end of the ramp. I have
included friction, but only kinetic friction. It seems to work fairly well
and reproduces the sorts of results which one expects and uses for Activity
Based Physics, including the published ILDs.
But there is the possibility of including static friction. The push is
generally fairly strong, so static friction would only come into play if the
cart stops. So there is one possible case where it might be different with
static friction.
Does static friction come into play during the instant when a cart reverses
direction after being kicked up the ramp? This would only have an effect if
the gravitational force component along the ramp is greater than kinetic
friction, and less than static friction. So can the kicked cart stop during
the turnaround because of this effect? I suspect that the static friction
may require a stationary period of time, but an instantaneous stop may not
be sufficient to fully activate the effect. I suspect the friction may
increase slightly during the turnaround, but no to the maximum static value.
This is a tricky experiment, but perhaps someone already has experience with
the answer.
I probably will not modify my simulation to take this into account, but
depending on the answer, who knows? Incidentally simulations can in some
cases be used to produce slightly better understanding than physical labs,
so they are a viable alternative to labs.