Gas station without pumps

2011 October 18

Physics Lab 4: spring constants

Filed under: home school — gasstationwithoutpumps @ 17:39
Tags: , , , ,

I had assigned the following lab assignment for this Friday, when I’ll be away in Washington, DC:

  1. Analyze the balldrop clips (in .mov format). For calibration, the distance we measured between the top and bottom stile of the file cabinet was 112cm. Since the ball was a few cm in front of the file cabinet, there may be some perspective error in using that measurement to calibrate the drop. Get Tracker to give you position, velocity, and acceleration plots. Use the fluctuation in the acceleration estimates to estimate the errors in the velocity and position measurements.
  2. Write a Vpython program that simulates the motion of the falling ball including the initial pause before dropping, but not including the bounces.

I still want to see the results of that, but it can wait another week to be turned in.  While I’m gone, I’d like a different lab done:

I have a box of 200 springs including 12 different types of extension springs.  What I want are measurements of all 12 springs, getting

  • relaxed length of spring (counting just the coil, not the loops on the end)
  • force (in N) required to extend spring by 1cm, 2cm, 3cm (or other appropriate lengths, depending how long the spring is and how stiff)
  • number of turns of coil
  • diameter of coil

Note: it might be good to select out one of each spring type and label them before starting the measurements, so that you don’t end up measuring the same spring type twice and missing one of the types.

For each spring, determine the following:

  • Is the force to extend the spring linear with the increased length for each spring?
  • If so, what is the spring constant (in N/m)?
  • What is the diameter of the wire for each spring? (This can be computed from the measurements above, or directly measured with a micrometer, or both.)

Finally, assuming that all 12 springs are made from the same material (which seems to be the case), come up with a model (a formula) that estimates spring constant given just the dimensions of the spring. (I have a model that I think they should follow, but the two of you will have to propose models and test them by plotting predicted vs. measured results.  I expect that the measurements will take about an hour, and that there will not be time during the lab to come to a conclusion on what model fits best—just time to discuss what models are worth trying and how to test the fit.

In addition to the box of springs, I’ll leave a hand-held digital force gauge, calipers, a micrometer, and a hook in the garage wall.  There are also various rulers and tape measures around. The force gauge is a very cheap one (under $10), so it is only calibrated in kg—you’ll have to covert to N.  The range (15kg) and precision (±5g) should be ample for this experiment.

 

4 Comments »

  1. […] Physics Lab 4: spring constants, I assigned a lab exercise to be done while I was away  in Washington, DC, measuring a dozen […]

    Pingback by Physics Lab 4: spring constants continued « Gas station without pumps — 2011 October 22 @ 11:38 | Reply

  2. […] I think I’ll make the students write up the modeling they’ll be doing of springs (see Physics Lab 4: spring constants and Physics Lab 4: spring constants continued).  I also had a good conversation about the physics […]

    Pingback by Home schooling weeks 5–8 « Gas station without pumps — 2011 October 25 @ 17:58 | Reply

  3. […] also want to see a write-up of the spring lab (Physics Lab 4), for which the students got the following […]

    Pingback by Physics update « Gas station without pumps — 2011 October 29 @ 11:02 | Reply

  4. […] Physics Lab 4: spring constants, I assigned a lab exercise to be done while I was away  in Washington, DC, measuring a dozen […]

    Pingback by Physics Lab 4: spring constants results « Gas station without pumps — 2011 November 9 @ 00:14 | Reply


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