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[O] Pure Physics Smart Guides

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  1. SECTION I: MEASUREMENT

    1. Physical Quantities, Units & Measurement
    7 Topics
  2. SECTION II: NEWTONIAN MECHANICS
    2. Kinematics
    8 Topics
  3. 3. Dynamics (Forces)
    7 Topics
  4. 4. Mass, Weight & Density
    4 Topics
  5. 5. Turning Effect of Forces
    4 Topics
  6. 6. Energy, Work & Power
    4 Topics
  7. 7. Pressure
    3 Topics
  8. SECTION III: THERMAL PHYSICS
    8. Temperature
    2 Topics
  9. 9. Kinetic Model of Matter
    2 Topics
  10. 10. Transfer of Thermal Energy
    5 Topics
  11. 11. Thermal Properties of Matter
    3 Topics
  12. SECTION IV: WAVES
    12. General Wave Properties
    3 Topics
  13. 13. Light
    7 Topics
  14. 14. Electromagnetic Spectrum
    2 Topics
  15. 15. Sound
    5 Topics
  16. SECTION V: ELECTRICITY & MAGNETISM
    16. Static Electricity
    5 Topics
  17. 17. Current of Electricity
    3 Topics
  18. 18. D.C. Circuits
    2 Topics
  19. 19. Practical Electricity
    4 Topics
  20. 20. Magnetism
    4 Topics
  21. 21. Electromagnetism
    3 Topics
  22. 22. Electromagnetic Induction
    4 Topics
Chapter 3, Topic 5
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Friction

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What is a friction?
Friction is the contact force that opposes or tends to oppose motion between surfaces in contact.

  • Opposes relative motion
  • Tendency towards motion
  • Static friction > kinetic friction

Advantages of Friction:

  • We can walk without slipping
  • Moving vehicles are able to slow down when needed

Disadvantages of Friction:

  • Cars are less efficient by up to 20%
  • Moving parts in engines, motors and machines suffer wear and tear

Ways to reduce friction:

  1. Lubricants / polished surfaces:
    Lubricants greatly reduce friction & wear & tear. Polishing a surface removes surface irregularities
  2. A layer of air/air cushion:
    Ex. Air hockey
  3. Ball bearings:
    Placed between moving parts, ball bearings roll around and prevent moving parts from rubbing against each other
  4. Wheels:
    Being circular in shape, wheels greatly reduce the friction between two surfaces

Uses of friction:

  • Treads (grooves in tyres that channel water out from underneath the tyres)
  • Parachutes (skydiver varies his air resistance to change his speed)
  • Chalk (absorb perspiration and improve grip)
  • Walking without slipping
  • Grip objects
  • Start an object moving

Classic Questions of Friction

1. Suggest and explain why a car moves at constant velocity after some time even though the car engine continues providing the same amount of forward driving force (thrust).

  • During acceleration, the car gains speed and the backward resistive forces (air resistance and contact friction with road) increases.
  • It comes to a point where backward resistive forces equals the forward driving force (thrust)
  • The resultant force acting on the object is now zero. Therefore the acceleration is zero and it continues moving with constant velocity (known as terminal velocity).