Re: The old loop-de-loop

[Bob Sciamanda <trebor@VELOCITY.NET>]

Ludwik asked:
>  . . . . . .. Here is the simple question that
> started our debate: Why does a constraint force appear
> (in the laboratory frame) when an object slides inside a
> vertical loop? Note that I did not ask how to calculate
> the constraint force; the question was qualitative.
Consider the same object sliding on a horizontal track and slamming into a
rigid, vertical wall, straight ahead in its path.  The molecules of the wall
are compressed together by the impact. Repulsive intermolecular forces (like
those of compressed springs) arise and grow, acting as a "force of
constraint" on the object, forbidding further forward motion of the object.

The object "hugging" a curved wall is also pushing against this constraining
wall, and forces of constraint arise  in exactly the same way.  The big
difference is that in the former case the constraining force is tangential
to the original object velocity and changes the object's speed - in the
second case the constraining force is normal to the velocity vector and
changes its direction.

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
http://www.velocity.net/~trebor/
trebor@velocity.net