physics- topic 9: forces and their effects

• How does gravitational attraction work?

  The larger mass gives greater attraction
• What happens with electrostatic attraction/repulsion?

  A larger charge gives greater force
• What do like charges do?

  Repel each other
• What do opposite charges do?

  Attract each other
• How does magnetic attraction/repulsion work?

  A stronger magnet gives a stronger field
• What do opposite poles do in magnetism?

  Attract each other
• What is the direction of the normal contact force?

  Perpendicular to the plane of contact
• How does friction work on rough surfaces?

  It causes resistance when moved
• What is a vector?

  A quantity with size and direction
• What is a scalar?

  A quantity with just size
• What are vector diagrams used for?

  • To show the direction of forces
  • To represent forces acting on an object
• What does a free body diagram illustrate?

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

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

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

  Downwards
• What is the center of mass?

  The point from which weight acts downwards
• What do scale drawings represent in vector diagrams?

  • Length of arrows represents size
  • Direction of larger arrows shows resultant force
• What happens if arrows in a vector diagram are equal in length but opposite in direction?

  The forces cancel out
• What does it mean if an object is in equilibrium?

  It travels at a constant velocity
• What are the functions of gears?

  • Change speed
  • Change force
  • Change direction by rotation
• What happens when a gear with fewer teeth is connected to a larger gear?

  The second gear turns faster with less force
• What happens when a gear with more teeth is connected to a smaller gear?

  The second gear turns slower with more force
• In which direction does the second gear always turn?

  In the opposite direction
• How does lubrication affect friction?

  It reduces friction and increases efficiency
• What conditions are necessary for rotation to occur?

  • An object attached to a pivot point
  • A force applied not towards the pivot
• What happens if a force is applied perpendicular to the object?

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

  Moment = Fd
• What is the unit of moment?

  Newton metre (Nm)
• How is the moment of a force calculated?

  Force times distance perpendicular to the direction
• What occurs when the sum of anticlockwise moments equals the sum of clockwise moments?

  Equilibrium occurs
• What is the effect of pressing your foot down on a bike pedal?

  • Causes a moment about the pivot
  • Turns the pedal arms