Chapter: Friction

• Introduction to Friction

  • Definition: Opposing force between two surfaces in contact
  • Nature: Acts opposite to the direction of motion
  • Cause: Irregularities on surfaces in contact

• Factors Affecting Friction

  • Nature of Surfaces
    • Rough surfaces: More interlocking, greater friction
    • Smooth surfaces: Less interlocking, lesser friction
  • Pressing Force
    • Greater weight/pressure increases friction
    • Lighter load decreases friction

• Types of Friction

  • Static Friction
    • Force required to overcome initial rest
    • Maximum among the three types
  • Sliding Friction
    • Force when an object slides over a surface
    • Slightly less than static friction
  • Rolling Friction
    • Force when an object rolls over a surface
    • Least among all types

• Friction: A Necessary Evil

  • Advantages (Friend)
    • Walking without slipping
    • Writing with a pen/pencil
    • Fixing nails and stopping vehicles
  • Disadvantages (Foe)
    • Wear and tear of shoes and machine parts
    • Generation of heat, causing energy loss

• Methods of Increasing and Reducing Friction

  • Increasing Friction
    • Using treaded tyres for better grip
    • Using brake pads in bicycles
    • Applying sand on slippery tracks
  • Reducing Friction
    • Using lubricants (oil, grease)
    • Using ball bearings (rolling replaces sliding)
    • Streamlining body shape (airplanes, fishes, cars)

• Fluid Friction (Drag)

  • Definition: Friction exerted by liquids and gases
  • Factors affecting drag:
    • Speed of the object
    • Shape of the object (streamlined reduces drag)
    • Nature of the fluid