Moments | Physics for GCSE/IGCSE - Year 11 PDF Download

Moments

• Forces can not only make objects speed up, slow down, change direction, and deform but also induce rotation.
• An instance of such rotational motion is when a force acts on one side of a pivot, causing the object to rotate either clockwise or anticlockwise.
  • The rotation direction can be clockwise or anticlockwise.

• A moment is described as:
  The rotational influence or torque produced by a force in relation to a pivot point.
• The size of a moment (M) is given by the formula: 
  M = F × d
• Here, 
  M represents the moment in newton metres (Nm),
  F is the force in newtons (N), and
  d is the perpendicular distance of the force to the pivot in meters (m).

• The door handle is typically placed opposite the hinge to increase the perpendicular distance from the pivot point.
  • This larger distance results in a greater moment or turning effect when force is applied, making it easier to open the door.
  • Conversely, having a handle close to the pivot would require much more force to open the door.
• Examples involving moments:
  • Using a crowbar to pry open something.
  • Turning a tap on or off.
  • Operating a wheelbarrow.
  • Using scissors.

Principle of Moments (Core)

• The concept of moments:
  If an object is in balance, the total clockwise moment around a pivot point equals the total counterclockwise moment around the same pivot point.
• Key points to remember:
  • The formula for moment is force multiplied by the distance from a pivot. The forces must act perpendicular to the distance from the pivot. For instance, on a horizontal beam, only forces directed upwards or downwards will create a moment.
  • Illustrative example: On a horizontal beam, forces causing a moment are those directed either upwards or downwards.

Principle of Moments (Extended)

• In the above diagram, Force F₂ is supplying a clockwise moment; Forces F₁ and F₃ are supplying anticlockwise moments.
• The mathematical representation of the principle of moments is F₂ x d₂ = (F₁ x d₁) - (F₃ x d₃).