Physics · Grades 8–11
Balance moments about a pivot
Use perpendicular lever arms; neglect the beam’s own weight in this model.
Rule and assumptions
Use perpendicular lever arms; neglect the beam’s own weight in this model.
F₁d₁ = F₂d₂
Worked examples
On a weightless balanced beam, 18 N acts 8 m left of the pivot. What downward force at 10 m right balances it? Forces are perpendicular to the beam. Round to 3 decimal places if needed. Answer in N.
F₁d₁ = F₂d₂ 18 × 8 / 10 = 14.4
14.4 N
On a weightless balanced beam, 51 N acts 6 m left of the pivot. What downward force at 3 m right balances it? Forces are perpendicular to the beam. Round to 3 decimal places if needed. Answer in N.
F₁d₁ = F₂d₂ 51 × 6 / 3 = 102
102 N
Try two questions
On a weightless balanced beam, 84 N acts 2 m left of the pivot. What downward force at 2 m right balances it? Forces are perpendicular to the beam. Round to 3 decimal places if needed. Answer in N.
On a weightless balanced beam, 45 N acts 8 m left of the pivot. What downward force at 5 m right balances it? Forces are perpendicular to the beam. Round to 3 decimal places if needed. Answer in N.
Answers and reasoning
Answers and marking notes
- 84 N
F₁d₁ = F₂d₂ 84 × 2 / 2 = 84
- 72 N
F₁d₁ = F₂d₂ 45 × 8 / 5 = 72
Further reading and review references
These are reference links, not copied exercises, institutional endorsement or proof of independent review.
Learning preview · independent educational and translation review required. Suggested grades are not official curriculum alignment.