Faster than 'g'?

1. NOTE: This is my original explanation. See addendum below for proper explanation! Place 11 pennies, or quarters if you are rich, on a meter stick with one coin at each 10 cm mark, including the 0 mark. Now, support the stick with two fingers, one at the 0 and one at the 100 mark. Suddenly remove the finger supporting the 100 mark and have kids observe what happens. This is a great demo to videotape and play back in slo-mo. Note; the 100 mark actually falls FASTER than 'g'. This is evident because it falls faster than the penny above it which is assumed to fall at 'g'! This is a seemingly impossible feat. However, realize that the center of mass of the stick falls at 'g'. The stick is ROTATING, thus the END moves faster than the pennies above it. From 0-50, the pennies stay in contact because everything is falling at or less than 'g'. Video this and show back at slowmo to analyze it.

   ADDENDUM 08/16/03: I knew my "textbook" explanation of this was too simplistic. However, I'm guilty of that most dreaded of all scientific/education guffaws; saying or hearing something so many times that you just accept it without even thinking! Coises, foiled again! Professor A. John Mallinckrodt of Cal Poly Pomona provided a much better physics explanation. In his own words copied from his email:

   Looking at the torque due to gravity around the supported end and setting it equal to the rotational inertia about the supported end times the angular acceleration, you find
   

   (mg)(L/2) = [(1/3)mL^2]*alpha
   so
   alpha = (3/2)*(g/L)
   Therefore, the initial acceleration of the CM is
   a_cm = alpha*(L/2) = (3/4)*g
   and the initial acceleration of the free end is
   a_free = alpha*L = (3/2)*g

   Thanks, John!

   
   
2. Get a film clip of a falling industrial chimney. This is the explanation of why they snap in half BEFORE they hit the ground. At the chimney begine to topple over, it's center of mass accelerates at 10m/s². This, however, tries to force the TOP of the chimney to accelerate FASTER than 'g'! This causes tremendous strain on the structure and it crumbles on the way down. Cool!