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400 Newtons to the Layman?

  1. Sep 10, 2008 #1
    I'm a middle school history teacher and I have to explain to a group of parents what 400 Newtons is. It's a long story...

    I've googled Newtons and understand that they're a measurement of force. It would be great if someone could give me some real world examples of what can produce a force of 400 Newtons.

    Is it like a brick falling off a building? Being hit in the head with a rock?

    Any help on this would be appreciated as the science teachers in my school are at a loss...
     
  2. jcsd
  3. Sep 10, 2008 #2

    ZapperZ

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    You can always use the weight equivalent.

    400 N is ~ 40 kg on the surface of the earth (with g ~ 10 m/s^2). This is approximately 88 pounds. So someone who weighs 88 lbs exert a force on the ground equivalent to 400 N.

    Zz.
     
  4. Sep 10, 2008 #3

    FredGarvin

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  5. Sep 10, 2008 #4
    So I could say that if I dropped a 90 pound student off the roof of the school, that would be the equivalent of 400 Newtons?
     
  6. Sep 10, 2008 #5

    Mapes

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    No, because the force of the student landing on you would depend on how fast they decelerate. Better to talk about suspending a 90 pound student in your arms or on a rope.

    I wonder if the pull from a large dog on a leash would be several hundred N, and if that might be more familiar?
     
  7. Sep 10, 2008 #6

    uart

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    I think you've got the wrong idea about force, you don't need rocks falling on peoples heads or students being thown off buildings to expain it. It's best explained simply in terms of how hard you need to "push" something. A force of 10 Newtons for example is the force you'd need to apply to hold approximately 1kg (2.2 pounds) against the force of gravity (at the Earths surface).

    For example, if you balance a 1kg object (say bag of flour or whatever) on the palm of your hand then the force with which your hand must push upwards, just to hold it still, is approximately 10 Newtons. Similarly 400 Newtons is equivalent to a mass of about 40kg (88 pounds) in the same situation.
     
  8. Sep 10, 2008 #7

    ZapperZ

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    No. An 88 lbs student standing still will exert a force (weight) equivalent to 400 N onto the ground. It means that if you put that student on a spring, the spring will experience a force of 400 N on it due to the weight of that student at equilibrium.

    Zz.
     
  9. Sep 10, 2008 #8
    Thanks for all the replies. I think I'll now be able to give a very clear explanation to the parents tonight.
     
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