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• Work:
  • Force acting on an object multiplied by displacement of object
  • W= F × s
  • SI Unit: Nm or J
  • Work done is zero if there is no displacement
• Positive and negative work:
  • Work done is positive if force acts along the direction of displacement
  • Work done is negative if force acts opposite to direction of displacement
• One Joule Work or One Unit Work: Work done when one newton force acts on an object and displace it by one meter.
• Energy:
  • Capacity to do work
  • SI unit: Joule (J)
  • One Joule of work take one joule of energy
• Forms of energy: Mechanical Energy, Heat Energy, Chemical Energy, Electrical Energy, Light Energy. Mechanical energy is classified into Kinetic Energy and Potential Energy.
• Kinetic Energy:
  • Object performing motion possess kinetic energy.
  • Mathematical Expression: E_K = ½ mv²
  • E.g: A moving car, a rolling ball, etc.
• Potential Energy: Energy possessed by an object due to its position.Click here to watch video on Kinetic Energy and Potential Energy
• Gravitational Potential Energy:
  • It is the work done in raising an object from the ground to the height, against the gravitational force.
  • Mathematical expression: E_p = mgh
• Conversion of Energy:
  • Energy is converted from one form to another.
  • E.g: When an object is released from a height, its potential energy is converted to kinetic energy, which provides motion to an object.
• Law of conservation of energy:
  • Energy is neither created nor destroyed, it is converted from one form to another, and total energy of the system remains constant.
  • Total energy (Kinetic energy + Potential energy) = Constant
  • ∴ mgh + ½ mv² = constant.
• Power:
  • It is rate of work done or rate of energy transferred.
  • SI unit: Watt (W)
  • Mathematical expression: P = W/t
• One Watt Power: One joule of energy used in one second
• Average Power: Total energy used by system divide by total time taken
• Commercial unit of energy:
  • For domestic or industrial purposes large amount of energy is used.
  • Unit kilowatt hour (kWh) is used to express such a large energy.
  • In electric bills, one unit is equal to one kilowatt hour
  • One kilowatt hour, is 1000 J of energy used by a machine in one hour.
  • Therefore, 1kWh = 1kW × 1 h
    = 1000W × 3600s..
    = 3600000 J
    1kWh = 3.6 × 10⁶ J