Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Experimental speed of sound

  1. May 27, 2010 #1
    1. The problem statement, all variables and given/known data
    For my physics lab, we have to calculate the speed of sound through steel and aluminum based on an experiment we did using a microphone and a program called Logger Pro. The resulting graphs gave the frequency of the sound of the aluminum rod as 2109.38 Hz, and the frequency of the sound of the steel rod as 2578 Hz. The aluminum rod is .995m, and steel rod is .987m. We are also told that the wave length is twice the length of the rod.

    2. Relevant equations
    velocity = wavelength * frequency

    3. The attempt at a solution

    v(aluminum) = (2*.995)*2109 = 4196.91 m/s
    The given value for the speed of sound through aluminum is 5100 m/s, so my experimental value is about 18% off of the actual value. Am I missing something, or is my data just poor?

    v(steel) = (2*.987)*2578 = 5088.97 m/s
    This value is also very off of the given value, which was 5960 m/s. So for this one, I have about a 15% error. Again, am I using the wrong equation, or is my data just poor?

    Note that I did not do the experiment, this was data given to the students by our instructor.
  2. jcsd
  3. May 27, 2010 #2
    Hello momopeaches.Every experiment is subject to errors and uncertainties and not being familiar with the method used in this experiment it is difficult to estimate what the overall percentage uncertainty should be.I am guessing that the fundamental frequencies were measured by subjecting the rods to a variable forcing frequency until resonance occured.Anyway you can only use the data you were provided with and it seems that you have done the calculations correctly.Make sure you don't present your answers with too many significant figures.
  4. May 27, 2010 #3
    Since I didn't do the experiment and was just given the data, its hard for me to say what the method used for the experiment were. In past labs, my group has usually been able to have a less than 5% error. The instructor wants us to explain who we may have gotten a high percent error, but without doing the experiment, its hard to say what may have been done wrong.

    Thank you for your reply. :) I've been sick for a couple weeks, so coming back and learning a whole chapter in a day makes me shaky on lab reports.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook