Contact and non contact force

• Gravitational Force


  • The force that pulls all objects towards the earth
  • Force of Gravity exists between any two objects with mass
  • Do not use the term gravity to refer to gravitational force - just like we do not use the term electricity to refer to current
• Electrostatic force

  • Electric charges that do not flow in an electric circuit are called static electricity
  • Unlike charges attract each other
  • Like charges repel each other
  • The force acting on the positive and negative charges is called the electrostatic force of attraction
  • The force acting on the negative charges is called the electrostatic force of repulsion
• Magnetic Force

  • A magnet can attract objects made from iron and steel
  • The magnet exerts a force called a magnetic force or magnetism
  • Magnetism is a non-contact force
  • A magnet has two poles - a north pole (N) and a south pole (S)
  • When like poles of two magnets face each other, the magnets repel each other
  • When unlike poles face each other, the magnets attract each other
  • Electromagnets are used to separate iron and steel from scrap metal piles
• Friction as a Useful force

  • Friction always opposes the movement of an object
  • Friction causes surfaces to heat up
  • Friction allows us to skate, walk, ride a bicycle, and write
  • Friction is needed to move a car
• The moon's gravity pulls on the water in the oceans

  Causing tides
• Uses of magnetic force in transportation

  • Separating iron and steel from scrap metal piles
• The moon's gravity is only about 1/6 the force of gravity of the earth
• Non-contact Forces


  • Magnetic force
  • Electrostatic force
  • Gravitational force
• Friction as a nuisance

  • Friction makes movement more difficult
  • Friction wears away materials
  • Air resistance slows down vehicles and causes greater fuel consumption
• Friction acts whenever one surface rubs against another surface
• Uses of electrostatic force

  • Causing hairs on arms and dust on the table to be attracted to plastic wrap
  • Magnetic levitation in 'Maglev' trains
• A contact force is a force that acts when objects touch. Friction is a contact force
• Air resistance slows down vehicles and causes greater fuel consumption
• Whenever an object is touched, contact forces act on it
• Contact forces

  • Frictional force
  • Tension force
  • Normal force
  • Air resistance / Drag force
  • Applied force
• Ways to reduce friction

  1. Using smooth surfaces, e.g. the lanes in a bowling alley

  2. Using ball bearings, e.g. moving parts of machines

  3. Using lubricants, e.g. moving parts of a bicycle

  4. Using streamlined shapes, e.g. aircraft
• Forces can be classified into 2 categories, Contact and Non-Contact Forces
• Friction

  • Acts in the opposite direction at the point of contact and provides the forward force that drives the car
  • Makes movement more difficult
  • Wears away materials
• Examples of contact forces include:

  Frictional force

  Tension force

  Normal force

  Air resistance / Drag force, Applied force
• Factors affecting frictional force

  • Roughness of the surfaces in contact; the rougher the surface, the greater the friction
  • Magnitude of the forces pressing the surfaces together (in the case of horizontal movement, the pressing force is the weight)
  • Independent of the area of contact
• Non-contact forces


  • Magnetic force
  • Gravitational force
• A force that acts on an object without any object touching it is called a non-contact force