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Homework Help: Physics Lab, Need help!

  1. Dec 4, 2013 #1
    So I received a lab today for physics. The first part of the lab I finished in about 20 minutes,had no trouble with it, but I don't understand what I'm doing wrong in the second part. I have to find the density of steel in excel, using experimental data that we found in class a few weeks ago.

    The diameter, mass, and volume of the sphere are correct. This is my data:
    Diameter Mass Volume
    3.97 0.36 8.31
    6.2 1.04 12.98
    9.4 3.52 19.68
    12.5 8.35 26.17
    13.45 10.02 28.16
    15.67 16.3 32.80

    But for the density I keep getting these numbers:

    The balls are made of steel, so obviously the density I found is incorrect. Can someone please tell me what I'm doing wrong. I know the density is mass/volume... I know that, so I don't know what I'm doing wrong.
    I'm sorry that the density and stuff are messed up, I dunno why physics forum did so
    Last edited: Dec 4, 2013
  2. jcsd
  3. Dec 4, 2013 #2


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    Staff: Mentor

    Hi TalRoc, http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

    All physical measurements in science have units associated with them, could you please indicate the units appropriate to your figures.

    I can guess how you might have measured the diameter, but how did you measure the volume?

    Roughly what value of density are you expecting you should get?
    Last edited by a moderator: May 6, 2017
  4. Dec 4, 2013 #3


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    Staff Emeritus
    Science Advisor
    Homework Helper

    I checked a few of the numbers from your experiment. If you have measured the diameter of the sphere, there should be some correlation with the volume. If these two numbers are using consistent units, then the formula for the volume of a sphere given the radius must have changed.
  5. Dec 4, 2013 #4
    Okay, so diameter is in cm, volume is in cubic centimeters.
    Also thanks for the quick reply!
  6. Dec 4, 2013 #5
    SteamKing, thanks for the help, but I still don't get why excel is coming up with those numbers.

    This is a screenshot of my excel document: http://gyazo.com/9aa4422a96414b614a2aa152563d50cf

    Please tell me what I'm doing wrong I'm really confused :/
  7. Dec 4, 2013 #6


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    Staff Emeritus
    Science Advisor
    Homework Helper

    According to the formula in the Excel spreadsheet, the volume of a sphere is (4/3)*pi*r. You might want to check that.
  8. Dec 9, 2013 #7
    Got it. I was making a stupid mistake the whole time and forgot to multiply by 1000 at the end...
    And I was wrong the units were mm and g. I see what I did now.

    Thanks guys
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