CONTENT NOT ON NOTES PAGE
Stable, unstable and neutral equilibrium
Torque is what is trying to topple you (i.e. rotate you against your will).
ETYMOLOGY: the word torque comes from Latin torquere, 'to twist'.
In many cultures, people carry heavy loads on their heads instead of their backs or hands. No torque that way, is easier, but requires balancing skill.
Leaning Tower of Pisa doesn’t topple because its CG is above its base. But it’s getting closer to the edge...
DEMO: Leaning Tower with a box.
DEMO: Use odd-shaped flat board to demo properties of the CG and how to locate the CG.
DEMO: What does "top-heavy" mean? Plug aluminum rod with brass weight (moment of inertia demo) into a wood base. Show and discuss how far the rod must be tilted in order to tip over, as a function of CG location and therefore brass weight location.
DEMO: Balancing hummingbird
DEMO: Balanced equal-mass balls and different-mass balls, hanging from ceiling.
DEMO: Why do wheels work? Catenary road.
DEMO: Have everyone stand on tiptoes. Your CG moves (usually unconsciously) forward to be over the point of support, which has moved forward. Try standing against and facing a wall and standing on tip-toes. Also, try standing with back to wall and touch toes. You become unstable.