Mistake Master · AP Physics C · Unit 2 · Topic 2.8 · Step-Through Animation
The Minus Sign Is the Physics
Stretch a spring and it pulls back in; compress it and it pushes back out. Hooke’s law writes that one rule as F = −k·Δx, and the minus sign is the whole point — it is “back toward equilibrium” in algebra. Watch the force flip sign at the natural length, hang a mass to find the settle point, then combine springs without swapping the series and parallel rules.
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