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S3.3 Power : the rate of working

Preamble

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Preamble

Time considerations are not involved in the definition of work. In many instances however it is necessary to consider the rate at which work is done, as well as the total amount of work accomplished.
 

[A] Definition

Commentary

Commentary

  • Avoid the misconception that there is something inherently electrical about the watt (or kilowatt)
  • Power may be used to define new units of work eg. One kilowatt-hour is the work done in one hour by a force working at the constant rate of one kilowatt.
  • Power is not just an abstract physical concept but has real monetary value (it can be bought and sold on the Stock Markets in units of kilowatt-hours!)
  • Using the definition of Work Equation 3.1 it is easy to show that

    $$ P=\vec{F}\cdot\vec{v} $$

 
TThe Power Generated by Two Lifts

Learning Resources

Textbook: HRW chapter 7.9
Course Questions:
Self-Test Questions: