SC 7.1

• Work, W

  • Work is done when a constant force applied on an object, cause the object to move in the same direction as the force applied
  • the product of the force, F, and the displacement, s, in the direction of the force, W = Fs.
  • S.I. unit used is joule (J) or metric unit newton meter (Nm)
  • One joule equals to the total amount of work done when one Newton of force is applied to move an object by 1 meter
  • The amount of work increase if
  • the force applied is large
  • the displacement of object is more
• Work is not done when

  • Force applied does not move the object
  • eg pushing a wall
  • Displacement to the direction of force is zero, so no work is done on the weight of the object
  • bringing objects with constant velocity

  In conclusion, work is not done when

  • The motion is perpendicular to the acting force
  • The force is applied upon the object but the object does not move
• Energy

  • Energy is the ability to do work
  • The total work done is equivalent to the amount of energy used to do the task
• Power

  • Power is the rate of work done in a unit of time
  • The metric unit for power is Watt (W) or Joule per second (J/s)
  • 1 watt is equivalent to one joule per second
  • Formula: Power (W) = Work (J) / Second (s)
• Horse power

  • The amount of work done by a horse in one second
  • 1 horse power = 735 watt
  • Horse power is a common term to a vehicle's efficiency
  • A higher horse power sums to a greater powered engine