Power

• Definition of Power:

  • Machines, such as car engines, transfer energy from one energy store to another constantly over a period of time
  • The rate of this energy transfer, or the rate of work done, is called power
• • Time is an important consideration when it comes to power
  • Two cars transfer the same amount of energy, or do the same amount of work to accelerate over a distance
  • If one car has more power, it will transfer that energy, or do that work, in a shorter amount of time
• Two cars accelerate to the same final speed, but the one with the most power will reach that speed sooner:

  
• Two electric motors:

  • lift the same weight
  • by the same height
  • but one motor lifts it faster than the other
  • The motor that lifts the weight faster has more power
• Two motors with different powers:

  
• • Power ratings are given to appliances to show the amount of energy transferred per unit time
• Power Rating Table:

  
• Calculating Power:

  • Power is defined asenergy transferred per unit time
  • And 

  work done = energy transferred

  • Therefore, power is also

  work done per unit time
• Where:

  • P = power, measured in watts (W)
  • E = energy transferred, measured in joules (J)
  • W = work done, measured in joules (J)
  • t = time, measured in seconds (s)
• Work, power, time formula triangle: