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Calculation help?

  1. Mar 21, 2010 #1
    Alright, well.
    How do I get mass out of pounds?
    I need to figure out what the force is in newtons on someone when they fall 1 meter.

    The person weighs 95 pounds.

    Do I need to convert it to kilograms then divide that by the gravitational constant of 9.81 m/s?

    or can I just do 95/9.81?

    1/1 = 1m/s^2

    0 ~ 1 / 1s = 1m/s^2

    9.7 x 1 = 9.7

    F = 9.7

    First I did speed, which was 1/1 (1 meter for 1 second) = 1m/s^2

    Then I did acceleration, and then M x A = 9.7

    Is it correct?

    NOTE: This is not homework.
  2. jcsd
  3. Mar 21, 2010 #2


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    Gold Member

    Pounds are units of force, like Newtons, so you'd convert them to Newtons first, then divide by the 9.81 [m/s^2]. Converting pounds to kilograms would be as meaningless as converting newtons to kilograms.

    The unit of mass in the US is called 'slugs'. I've never seen them used before personally. But you could convert slugs to kilograms.
  4. Mar 21, 2010 #3

    How do I convert them to newtons? I did

    95/ 9.81 = 9.7

    so isn't the force 9.7 newtons? or how do i get newtons?
  5. Mar 21, 2010 #4


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    Gold Member

    The equation is:

    F = ma
    (force) = (mass)*(acceleration)

    some examples of this in both systems:

    newtons = (grams) * (meters/second^2)


    pounds = (slugs)*(miles/hour^2)

    In this case, the acceleration a is g, so a = g.

    So F = mg, therefore, the force is your value before dividing by g. So, as I said, convert the force from pounds to newtons, then divide by gravity.

    You can easily do this conversion by typing "x pounds in newtons" into google
  6. Mar 21, 2010 #5
    lol I'm not really understanding, its only possible for me to learn if someone does the whole calculation and I can actually see it.

    Can you do it for me?

    The object is falling for 1 second and went 1 meter in that 1 second.

    I want to know the force that it hits the ground.

    can you show all the math please?
  7. Mar 21, 2010 #6


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    Homework Helper

    The normal unit of mass in english units is a slug, but it's common to specify "pound mass" as opposed to "pound force". The weight of a person is commonly expressed in pounds (force) or in kilograms (mass), without causing confusion. To answer your question:

    1 pound_mass = 0.45359237 kilograms
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