Specific forces

• Friction


  A force that opposes motion and always acts in the direction opposite to the motion
• Without any forces acting on it, an object in motion would continue moving forever (e.g. a ball kicked in outer space)
• Scenarios


  • Object at rest with net force zero (book on table)
  • Object in motion with net force zero (object in absence of friction or gravity)
  • Object at rest with net force greater than zero (ball kicked)
  • Object in motion with net force not zero (car with gas pedal pressed)
• Speed


  Calculated as distance divided by time