Forces & their effects

• What is an example of interaction of objects at a distance without contact?

  Gravitational attraction
• How does gravitational attraction depend on mass?

  The larger mass gives greater attraction
• What happens when two like charges interact?

  They repel each other
• What is the relationship between charge and force in electrostatic interactions?

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

  Like poles repel, opposite poles attract
• How does the strength of a magnet relate to its field?

  A stronger magnet gives a stronger field
• What is the normal contact force?

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

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

  A vector has size and direction
• Give an example of a vector.

  Weight, velocity, force, or displacement
• What is a scalar?

  A scalar has just size
• Provide examples of scalars.


  Mass, distance, speed
• What do free body diagrams show?

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

  It acts at the normal to the line of contact from the point of contact
• How does friction behave in relation to movement?

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

  Downwards, acting from the Centre of Mass
• What does the length of each arrow in a vector diagram represent?

  The size of the force in relation to other forces acting on the object
• What happens when arrows in a vector diagram are equal in magnitude but opposite in direction?

  The forces cancel out, and the object is in equilibrium

  
• What is terminal velocity?

  It is reached when weight and air resistance are equal and balanced
• What occurs when a skydiver initially jumps from a height?

  Initially, the only force acting on him is weight
• How does air resistance change as a skydiver falls?

  It increases as he accelerates, increasing his speed
• What is the relationship between force, mass, and acceleration as described by F=ma?

  As the resultant force decreases, acceleration decreases
• What happens to a vehicle's thrust as air resistance increases?

  It decreases the resultant force
• What is the condition for a vehicle to travel at terminal velocity?

  Thrust is balanced by drag and friction, resulting in no resultant force
• What is required for rotation to occur?

  An object must be attached to a pivot point
• What happens when a force is applied not towards the pivot point?

  The object will not rotate and will just be held still
• What is the effect of applying force perpendicular to an object?

  The object will move about the pivot in that direction
• How do you find the moment of a force?

  Moment = $F \cdot d$
• What is the unit of moment?

  Newton metre (N m)
• How does pressing your foot down on a bike pedal create a moment?

  It causes a moment about the pivot, turning the pedal arms
• What condition must be met for equilibrium to occur?

  Sum of anticlockwise moments = sum of clockwise moments
• How do gears affect speed, force, or direction?

  Gears can change speed, force, or direction by rotation
• What happens when the first gear is connected to a smaller gear?

  The second gear will turn faster but with less force
• What occurs when the first gear is connected to a larger gear?

  The second gear turns slower with more force
• In what direction does the second gear always turn when connected to the first gear?

  In the opposite direction
• How does lubrication affect energy transfer?

  It reduces friction, so reduces unwanted energy transfer and increases efficiency
• What are the key points about object interaction at a distance and with contact?

  • At a distance:
  • Gravitational attraction
  • Electrostatic attraction/repulsion
  • Magnetic attraction/repulsion
  • With contact:
  • Normal contact force
  • Friction
• What are the characteristics of vectors and scalars?

  • Vectors:
  • Have size and direction
  • Examples: weight, velocity, force
  • Scalars:
  • Have only size
  • Examples: mass, distance, speed
• What are the rules for free body diagrams?

  • Reaction force acts at the normal to the line of contact
  • Friction acts opposite to movement
  • Weight acts downwards from the Centre of Mass
• What are the conditions for equilibrium in a system?

  • Forces cancel out when equal in magnitude but opposite in direction
  • Sum of anticlockwise moments = sum of clockwise moments