ME: …so, in all of your pulley experiments, we find that you needed a larger amount of force to lift the weights than you expected from the calculations. Why do you think that is?
TEN-YEAR-OLD: I don't know.
ME: Well, what's the difference between an ideal imaginary pulley and a real experimental pulley?
TEN-YEAR-OLD: …
ME: Something the real pulley has that the imaginary pulley doesn't. We talked about this, remember?
TEN-YEAR-OLD: …
ME: One word. Starts with "F."
TEN-YEAR-OLD (desperately): Flammable!
ME: …
TEN-YEAR-OLD: Real pulleys are flammable, you know.
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