Topic 9-Forces and their Effects

• How does gravitational attraction depend on mass?

  The larger mass gives greater attraction
• What happens with electrostatic charges of the same type?

  Like charges repel
• What is the effect of a larger charge in electrostatics?

  A larger charge gives greater force
• What is the behavior of magnetic poles?

  Like poles repel, opposite poles attract
• What does a normal contact force do?

  The force is perpendicular to the plane of contact
• What causes friction between surfaces?

  Rough surfaces cause friction when moved
• What defines a vector quantity?

  A vector has size and direction
• What does a free body diagram show?

  The direction of forces present in a situation
• What does the reaction force do in a contact situation?

  Acts at the normal to the line of contact
• How does friction act in relation to movement?

  Friction acts in the opposite direction to movement
• In which direction does weight always act?

  Downwards
• What does the length of an arrow in a vector diagram represent?

  The size of the force in relation to others
• What happens when two forces are equal in magnitude but opposite in direction?

  The forces cancel out
• What is equilibrium in terms of forces?

  Sum of forces equals zero
• What happens to a skydiver as they fall?

  Initially, only weight acts on them
• What occurs as a skydiver accelerates?

  Air resistance increases with speed
• What happens when weight and air resistance are equal for a skydiver?

  No resultant force and terminal velocity is reached
• What is terminal velocity in a vehicle?

  Thrust is balanced by drag and friction
• What is required for rotation to occur?

  An object must be attached to a pivot point
• What happens when a force is applied perpendicular to an object?

  It will move about the pivot
• How is the moment of a force calculated?

  $\text{Moment} =$$Fd$
• What unit is used for moment?

  Newton metre (N m)
• What occurs in equilibrium regarding moments?

  Sum of anticlockwise moments equals clockwise moments
• How do gears affect speed and force?

  Gears can change speed, force, or direction
• What happens when a smaller gear is connected to a larger gear?

  The smaller gear turns faster but with less force
• What is the effect of lubrication on gears?

  Reduces friction and increases efficiency
• What are the key points about forces acting on a skydiver?

  • Initially, only weight acts on the skydiver
  • As they fall, air resistance increases
  • Eventually, weight and air resistance balance
  • Terminal velocity is reached with no acceleration
• What are the key points about forces acting on a vehicle?

  • Initially, low air resistance and thrust
  • Air resistance increases, decreasing resultant force
  • Terminal velocity occurs when thrust balances drag and friction
  • More thrust changes the resultant force until balance is restored
• What are the principles of rotation in physics?

  • Rotation occurs about a pivot point
  • Force must be applied not towards the pivot
  • Perpendicular force causes movement about the pivot
  • Non-perpendicular force requires finding perpendicular distance
• What are the effects of gears in mechanical systems?

  • Gears can change speed, force, or direction
  • Smaller gears turn faster with less force
  • Larger gears turn slower with more force
  • Gears always turn in opposite directions
• What are the effects of lubrication in mechanical systems?

  • Reduces friction
  • Decreases unwanted energy transfer
  • Reduces heat loss
  • Increases efficiency