Teaching Physics with the Physics Suite

Edward F. Redish

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Free fall acceleration

Your roommate peeks over your shoulder while you are reading a physics text* and notices the following sentence: "In free-fall the acceleration is always g and always straight downward regardless of the motion." Your roommate finds this peculiar and raises three objections:

  1. If I drop a balloon or a feather, it doesn't fall nearly as fast as a brick.
  2. Not everything falls straight down; if I throw a ball it can go sideways.
  3. If I hold a wooden ball in one hand and a steel ball in the other, I can tell that the steel ball is being pulled down much more strongly than the wooden one. It will probably fall faster.
How would you respond to these statements? Discuss the extent to which these invalidate the quoted statement. If they don't, explain why.

* Physics, by E. Hecht (Brooks Cole Publishers, 1994)

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Page last modified September 30, 2002: D03