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1.4.1States of Matter

Moments — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 28 of 30 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Section 1 of 5Moment Basics

A moment is the turning effect of a force, and it depends on both the force and where it acts.

Moment
  • Moment The turning effect of a force about a pivot, calculated as force multiplied by perpendicular distance.
Pivot
  • Pivot The fixed point about which an object rotates when a moment acts on it.
Perpendicular distance
  • Perpendicular distance The shortest distance from the pivot to the line of action of the force.
Clockwise
  • Clockwise A turning effect in the same direction as the hands of a clock about the pivot.
Unit
  • Unit Moments are measured in newton metres, written N m.

Section 2 of 5Calculating a Moment

Converting to SI units before multiplying prevents most errors in this topic.

1
Identify the force in newtons and the perpendicular distance from the pivot in metres.
2
Convert any distance given in centimetres into metres by dividing by 100.
3
Multiply the force by the perpendicular distance to find the moment.
4
Give the answer in newton metres and state whether the turning effect is clockwise or anticlockwise.

Section 3 of 5Everyday Uses

Everyday Uses
Spanner
  • Spanner A longer spanner gives a larger moment for the same force, so a tight bolt is easier to turn.
Door handle
  • Door handle A handle far from the hinge needs less force to open the door than one close to it.
See-saw
  • See-saw A child further from the pivot can balance a heavier adult sitting closer to it.
Crowbar
  • Crowbar Using a long lever increases the distance and reduces the force needed to lift a heavy load.

Section 4 of 5Worked Example

Question

  • A spanner is 0.25 m long.
  • A force of 40 N is applied at its end, perpendicular to the spanner.
  • Calculate the moment about the bolt.

  1. Force F = 40 N and perpendicular distance d = 0.25 m.
  2. Moment = F × d = 40 × 0.25.
  3. Moment = 10 N m.

Answer The moment about the bolt is 10 N m.

Section 5 of 5Exam Checklist & Tips

1.4.1 – Key Points for the Exam

  • Moment The turning effect of a force, equal to force multiplied by perpendicular distance from the pivot.
  • Pivot The point about which an object turns.
  • Perpendicular distance The distance measured at right angles from the pivot to the line of the force.
  • Newton metre The unit of moment, written N m.
  • Turning effect The tendency of a force to rotate an object about a pivot.

Common Mistakes

  • Using a distance measured along the object rather than the perpendicular distance from the pivot.
  • Forgetting to convert centimetres into metres before calculating the moment.
  • Writing the unit of moment as N instead of N m, which is a different quantity.
  • Stating that a moment depends only on the force, when the distance from the pivot matters too.

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