bullet2 Are you working?

How do you determine if work has been done?  In science, specific conditions have to be met to determine work done.

bullet3 Objectives

At the end of this lesson, there will be a short quiz that will ask you questions about these objectives and you should be able to write a response to each of the statements below:
  • Define work.
  • Calculate the work done on a given object.
  • Recognize the SI units involved in measuring work.

bullet3 Scientific Definition

Work   is a quantity that measures a force acting on an object over a distance.

  • What's The Difference?
    So in the everyday world, if we say that we are going to work, we may not being doing work in the scientific definition.  In order to determine if work is being done, you need to think about the object on which a force is being applied.  

    • Working as Science Sees It
      Let's think about a weight lifter.  If a weight lifter is holding a barbell steady over his head, he is not doing any work.  The barbell is the object on which he is applying a force, but he is not moving the barbell over a distance.  He is holding it still over his head, so since the weight is not moving, there is no work done.  

      The lifter did do work as he lifted the barbell from the floor and over his head.  

      • Here Are The Conditions
        So if you are trying to determine whether work is being done, you need to be aware of what is happening to the object.  Is a force   being applied and does that force cause movement ?  If so,  then work is being done.


bullet3 Measuring Work

"I did more work than you!"   "No way, I did more!"

Can the amount of work done be measured?  Sure!  As with any physics concept, there is an equation that lets us put in known measurements to determine an unknown value.  Let's look at measuring work.

  • Work Equation
    Work is calculated as force times distance.  
    W = Fd
    Look at each of the pictures.  
    Force is being applied to objects to move them a distance.  
    The forklift will apply a force to move the stack of wood across the lumber yard.  

    The shopper will apply a force to move the cart and the groceries down the grocery isle.

    • SI Unit for Work
      Work is measured in units of newtons times meters.
        You should remember that the SI unit for force is newtons and that a newton is a derived unit (1kg x 1m = 1N).

      The unit for work is also a derived unit.  Work is measured in joules (J).  A joule is equal to 1kg x m2/s2 .

      1N x m = 1J = 1kg x m2/s2

      Since all of these units are equal, you can use any of the above units when solving work problems.  This will make canceling out other units in the problem much easier.
      It's time to begin solving work problems.