Work and Energy

• Work requires energy
• Work is done when a force produces motion in a body
• Conditions for work to be done:

  • Force should be applied on the body
  • Body should be displaced
• Work done in moving a body = Force × Displacement

  Work is a scalar quantity
• Unit of work is Newton meter or Joule

  1 Joule = 1 Newton × 1 meter
• Factors affecting the amount of work done:

  • Magnitude of force
  • Displacement
• Work done by a force can be positive, negative, or zero

  • Positive work: force acts in the direction of motion
  • Negative work: force acts opposite to the direction of motion
  • Zero work: force acts at right angles to the direction of motion
• Energy is the capacity of doing work
• Energy is a scalar quantity

  SI unit of energy is Joule (J)
• Mechanical energy is the sum of kinetic energy and potential energy of a body
• Kinetic energy is the energy of a body due to its motion

  • Kinetic energy is directly proportional to mass and the square of velocity
• Potential energy is the energy of a body due to its position or change in shape
• Unit of power:

  • SI unit of power is Watt (W) = 1 Joule/second
  • 1 Watt (W) = 1 Joule / 1 second = 1 J / 1 s
  • Average power = Total work done or total energy used / Total time taken