Contact and non-contact forces

• Forces are responsible for all interactions between particles and objects
• Forces can be divided into two categories: contact forces and non-contact forces
• Contact forces:

  • Force exerted between two objects when they are touching
  • Examples include reaction force, tension, friction, and air resistance
• Reaction force:

  • Force exerted in the opposite direction to an action force
  • Example: a book on a table
• Tension:

  • Pulling force exerted by each end of an object such as a string or rope
  • Example: a cable holding a ceiling lamp
• Friction:

  • A force that opposes or prevents movement and converts kinetic energy into heat
  • Example: a box sliding down a slope
• Air resistance:

  • A force of friction produced when an object moves through the air
  • Example: a skydiver falling through the air
• When a contact force acts between two objects, both objects experience the same size force, but in opposite directions. This is Newton's Third Law of Motion
• Non-contact forces are forces that act between two objects that are not physically touching each other
• Examples of non-contact forces include:

  • Magnetic force
  • Electrostatic force
  • Gravitational force
• Magnetic force:

  • Experienced by any magnetic material in a magnetic field
  • Opposite magnetic poles attract each other
  • Like magnetic poles repel each other
• Electrostatic force:

  • Experienced by any charged particle in an electric field
  • Opposite charges attract each other
  • Like charges repel each other
• Gravitational force:

  • Experienced by any mass in a gravitational field
  • Masses are attracted towards each other by gravitational force