1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Class 1 Lever Experiment: Wrong results

  1. Oct 6, 2014 #1
    Hey guys, I really need help with this, I do not understand what I did wrong in this experiment.

    I had a 30 cm ruler as a beam and some weights of 50 grams, 5 grams and 25 grams. I had a fulcrum which was 17 cm high. As you can see I only have measurements in 50, 5 and 25 grams. So I cut out some random paper, scrunched them into balls to make my lever balance at different lengths.

    However, the results the made my lever balance did not match the results I got from the equation:

    Effort force = Load force x load arm / effort distance.

    Could someone please tell some factors that affected my experiment results and why it didn't match the equation.

  2. jcsd
  3. Oct 6, 2014 #2


    User Avatar
    Science Advisor

    The equation assumes ideal circumstances. A real experiment is rarely so simple. You should be able to come up with some ways that the experiment doesn't match the ideal model.
  4. Oct 6, 2014 #3
    Agreed, but what are the factors that makes it not ideal?
  5. Oct 6, 2014 #4


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Sorry if this is a really obvious suggestion but....

    Rulers have zero at one end, not at the fulcrum. So when you worked out the "load arm" and "effort distance" did you calculate the distance from the fulcrum or just write down the number on the ruler?
  6. Oct 6, 2014 #5


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Actually, you can take moments about any point. But if you don't take the mid(balance ) point of the ruler, you have to include the weight of the ruler and the calculation is more long winded. For an easier result, you must do as CWatters suggests and relate everything to the mid point. You need to take your distance measurements carefully if you want your sums to 'balance' too.
  7. Oct 6, 2014 #6


    User Avatar
    Science Advisor

    A "30 cm ruler" in the U.S. is very likely 12 inches long -- 30.48 cm. If you were to use the 15 cm marker as the nominal midpoint then your measured moment arms would all be off by 0.24 cm. If you were to use the 15 cm marker as the fulcrum then you would have an additional 0.48 cm of ruler unaccounted-for at one end.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook