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Physics Concepts! Force and Work Help!

  1. Feb 11, 2010 #1
    1. The problem statement, all variables and given/known data
    1. What type of energy is involved in weighing something on a spring scale?
    2. What type of energy is involved in winding a watch?
    3. Is a machine's efficiency increased if the work done against the resistance force is decreased or if you decrease the work against friction?
    4. Is the amount of work decreased if the efforts needed are multiplied or if the effort distances are multiplied? (either, both, or neither).

    2. Relevant equations

    F=ma

    3. The attempt at a solution
    I cannot seem to grasp these concepts! Any help would be greatly appreciated! :)
     
  2. jcsd
  3. Feb 11, 2010 #2
    i prefer to help people understand the concept than flat out tell you the answer, so ill give you some pretty substantial help with 2. because that is a good starting point.
    when YOU wind up a watch you are effectively giving it energy to "work" for a period of time in the future. assuming youre winding a pretty old watch they have a spring inside that helps keep the time.
    Now you as a person has to actually wind the watch, and in order to create the energy used by your body you eat food, which then releases chemicals into the body and these chemicals are used, so the first step is CHEMICAL ENERGY.
    you are then using this chemical energy to power your fingers to wind the watch, therefore creating KINETIC ENERGY or movement.
    this then transfers into the watch to keep it ticking. seeing as this energy is stored by the spring in the watch you have given the watch POTENTIAL ENERGY, so that it can continue working into the future.

    hopefully this has broken it down enough for you :)
    hit back if you need more help
     
  4. Feb 11, 2010 #3
    Thanks for the help!!! Now, would weighing fruit on a spring scale be elastic potential energy also? That was my initial thought, but I then realized that the main focus on a scale is the mass, which is only in an equation for GRAVITATIONAL potential energy...
     
  5. Feb 11, 2010 #4
    there would be elastic potential, and i would suppose that if the spring balance was above ground it would have gravitational potential too, but i dont think that its key to state it as part of the answer to that question.
    The main focus of the scale is mass, and the mass being pulled by gravity exerts a downward force on the scale, thus stretching the spring and giving it elastic potential
     
  6. Feb 12, 2010 #5
    Thank you sooooo much for all of your help! I think I understand these concepts now :)
     
  7. Feb 12, 2010 #6
    no worries :)
     
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