Moments (Cambridge O Level Physics)

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Moments

 

  • As well as causing objects to speed up, slow down, change direction and deform, forces can also cause objects to rotate
  • An example of a rotation caused by a force is on one side of a pivot (a fixed point that the object can rotate around)
    • This rotation can be clockwise or anticlockwise

Pivot Point on a Metal Bar

pivot-force, IGCSE & GCSE Physics revision notes

The force will cause the object to rotate clockwise about the pivot

  • moment is defined as:

The turning effect of a force about a pivot

  • The size of a moment is defined by the equation:

M = F × d

  • Where:
    • M = moment in newton metres (Nm)
    • F = force in newtons (N)
    • d = perpendicular distance of the force to the pivot in metres (m)

Moment of a Spanner

moment-of-force, IGCSE & GCSE Physics revision notes

The moment depends on the force and perpendicular distance to the pivot

  • This is why, for example, the door handle is placed on the opposite side to the hinge
    • This means for a given force, the perpendicular distance from the pivot (the hinge) is larger
    • This creates a larger moment (turning effect) to make it easier to open the door

  • Opening a door with a handle close to the pivot would be much harder, and would require a lot more force

  • Some other examples involving moments include:
    • Using a crowbar to prize open something
    • Turning a tap on or off
    • A wheelbarrow
    • Scissors

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Leander

Author: Leander

Expertise: Physics

Leander graduated with First-class honours in Science and Education from Sheffield Hallam University. She won the prestigious Lord Robert Winston Solomon Lipson Prize in recognition of her dedication to science and teaching excellence. After teaching and tutoring both science and maths students, Leander now brings this passion for helping young people reach their potential to her work at SME.