P8 Forces in Balance

• What do scalar quantities have?

  Only a magnitude
• What do vector quantities have?

  Magnitude and direction
• What is the effect of multiple forces acting along the same line?

  They can be replaced by a resultant force
• How is the resultant force calculated when forces act in the same direction?

  • Sum of the magnitudes of the forces
• How is the resultant force calculated when forces act in opposite directions?

  • Difference between the magnitudes of the forces
• What does it mean if the resultant force on an object is zero?

  The forces are balanced
• How can scale drawings be used in force analysis?

  To find the resultant of two non-aligned forces
• How are forces represented in scale drawings?

  Drawn end to end
• What forms a triangle in scale drawings of forces?

  The resultant drawn between the two ends
• What is the parallelogram of forces used for?

  To resolve two forces drawn to scale
• What can a single force be resolved into?

  Two component forces at right angles
• What do the two component forces represent?

  Same effect as the single force
• What is the turning effect of a force called?

  Moment of the force
• How is the moment of a force calculated?

  $M =$$F \times d$
• What is true about moments in a balanced object?

  Clockwise moments equal anticlockwise moments
• How do levers and gears affect moments?

  They increase the moment of a force
• What happens when a small gear drives a large gear?

  Moment is increased, but moves slower
• How does a lever help in applying force?

  Allows force to be applied further from pivot
• What is a force?

  A push or pull on an object
• Are forces scalar or vector quantities?

  Vector quantities
• What are contact forces?

  Forces when objects are touching
• Give examples of contact forces.

  Friction, air-resistance, tension
• What are non-contact forces?

  Forces acting at a distance
• Give examples of non-contact forces.

  Gravitational, electrostatic, magnetic
• What are the key characteristics of force pairs according to Newton's Third Law?

  • Act on separate objects
  • Same size
  • Opposite directions
  • Same type
• What does Newton's First Law state?

  Velocity changes only if resultant force acts
• What happens to a stationary object if the resultant force is zero?

  It remains stationary
• What happens to a moving object if the resultant force is zero?

  It continues moving at the same velocity
• What do free body diagrams represent?

  Forces acting on a single object
• How are forces represented in free body diagrams?

  As arrows showing magnitude and direction
• What is the definition of centre of mass?

  • Point through which weight acts
• How is the centre of mass determined for a flat symmetrical object?

  Where the axes of symmetry meet
• How is the centre of mass found for an irregularly shaped object?

  By suspending from different points
• What does Newton's Third Law state about forces?

  They exert equal and opposite forces
• What is true about the size of interaction pairs of forces?

  They are the same size
• What is true about the direction of interaction pairs of forces?

  They act in opposite directions
• What type of forces are interaction pairs?

  Same type of forces
• What is the resultant force on a balanced object?

  Zero
• What is the centre of mass for a flat symmetrical object?

  Where the axes of symmetry meet
• What is the turning effect of a force called?

  Moment