CONTENT NOT ON NOTES PAGE
DEMO: rub block on table; image with thermal IR camera to see the generated heat
DEMO: force probe pulling a weight across the table. Applied force gradually increases, reaches max value before dropping to a lower constant force needed to move block with constant speed.
DEMO: normal force by electronic scale. Tilting the scale reveals reduced normal force.
JOKE: Q: Two cats are on a roof. Which slides off first? A: The one with the smaller mew (mu).