NapkinCalc

Statics — Forces & Equilibrium

Moments — the turning effect of a force

continues from lesson 2 — values defined earlier in the course stay live here

Free-body diagram: every force on the box drawn as an arrow — the language of statics.
Free-body diagram: every force on the box drawn as an arrow — the language of statics.

ELI5: push a door near the hinge and nothing happens; push at the handle and it swings. The turning effect is the moment = force × distance from the pivot. A balanced seesaw is two moments cancelling: F₁·d₁ = F₂·d₂.

Fkid:=300NF_{kid} := 300 N = 300 N a child on one side
dkid:=1.5md_{kid} := 1.5 m = 1.5 m how far out the child sits
Fdad:=800NF_{dad} := 800 N = 800 N a parent on the other side
ddad=Fkid⋅dkidFdadd_{dad} = \frac{F_{kid} \cdot d_{kid}}{F_{dad}} = 0.5625 m where the parent must sit to balance ≈ 0.56 m
✓ pass abs(Fdad∗ddad−Fkid∗dkid)<1e−6N∗mabs(F_{dad} * d_{dad} - F_{kid} * d_{kid}) < 1e-6 N*m the two moments cancel — the seesaw is level

Real-world hook: the same balance sizes a counterweight on a crane, the trim of an aircraft, and how far you can walk out on a diving board before it tips.