PHYSICS WORTH SHARING
You're in a car that turns left. Your body feels shoved right.
That shove isn't a force. It's your brain lying to you.
Big idea
The door (or seatbelt) pushes you inward so you turn with the car. No inward push, and you'd go straight through the curve.
"Centrifugal force" is just inertia wearing a costume: you want a straight line while the car bends underneath you. Same trick with a coin on a spinning paper plate — it looks flung out; it's really going straight while the plate curves away.
Watch Shawn's 60-second ghost-force short before class.
Try this (2 minutes)
For: Forces / circular motion. Materials: paper plate + coin.
Coin near the center of a plate on a smooth table.
Ask: "Will the coin feel an outward push when I spin?"
Spin. Path vs the room ≈ straight; vs the plate ≈ outward.
Land it: real force in a turning car = inward. Outward shove stays off the free-body diagram.
Summary
Outward shove ≠ outward force.
Real contact force points inward.
Ghost force = inertia when the path bends.
Shawn's Footnote
An outward "centrifugal" arrow on the classroom free-body diagram is already wrong. Inertial frame only: the passenger wants straight; the door (or seatbelt, or friction) is the force that turns them. Feeling ≠ second force.
Forward this to a colleague who still draws the outward arrow.
Stay Wildly Curious,
Lauren & Shawn
