Solve Physics Lab: Hooke's Law & Simple Harmonic Motion

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Discussion Overview

The discussion revolves around a physics lab focused on Hooke's Law and Simple Harmonic Motion, specifically addressing the calculation of the spring constant (k) based on experimental data. Participants are attempting to identify errors in the calculations and clarify the methodology used in the lab report.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses frustration over their lab grade and seeks feedback on their calculations related to spring elongation and the determination of k.
  • Another participant suggests that there may be labeling issues on the graph and questions whether the weight should already be in Newtons, implying that the conversion might be unnecessary.
  • A different participant points out that the values provided in the table are already multiplied by 9.81 m/s², indicating that the correct conversion to Newtons only requires multiplying by 0.001 to convert grams to kilograms.
  • One participant asserts that the correct value for k should be 20 N/m, based on their interpretation of the data and calculations.
  • Another participant clarifies that the initial mass values are indeed in grams and that the conversion to Newtons involves multiplying by g after converting to kilograms, defending their approach to the calculations.
  • The original poster asks for further suggestions after clarifying their understanding of the mass and force conversions.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the interpretation of the mass values and the correct method for calculating k. There is no consensus on the correct approach or the source of the discrepancy in the calculated values.

Contextual Notes

There are unresolved assumptions regarding the labeling of mass and force in the original data, as well as the correct application of conversion factors. The discussion reflects varying interpretations of the experimental setup and calculations.

kashmirekat
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I had a physics lab for Hooke's Law and Simple (ha!) Harmonic Motion. I am not pleased with my grade, but my professor did not indicate what I did wrong and I am banging my head against the wall trying to figure it out (btw, it's not helpful). So if any of you all can take a gander at it and tell me hey! You did this wrong! That would be great. Thank you.

First Section: Spring Elongation

weight(grams)*9.18m/s^2 | Scale reading (mm)
m1g = 114.26                  | y1 4.7
m2g = 124.26                  | y2 = 5.2
m3g = 134.26                  | y3 = 5.9
m4g = 144.26                  | y4 = 6.3
m5g = 154.26                  | y5 = 6.7
m6g = 164.26                  | y6 = 7.3
m7g = 174.26                  | y7 = 7.8
m8g = 184.26                  | y8 = 8.2

---
Okay, the first thing I did was convert the grams to kg and multiply by g (9.8m/s^2).
For these values I got:
mg1=1.12N, mg2=1.22N, mg3=1.3157N, mg4=1.414N, mg5=1.512N, mg6=1.61N, mg7=1.708N, mg8=1.806N

Then I converted mm to m...0047, .0052, .0059, .0063, etc.

It's asking for k and in parentheses next to it has slope of graph. [ie k(slope of graph)] So k=slope of graph. Slope equals rise/run, (delta y)/(delta x). So I choose two points 1 & 4.
(1.12N - 1.414N) / (.0047m - .0063m) = -0.294N / -.0016m = 183.75 N/m.

His answer is k = 20. Where did go wrong to get a value so far from the answer?
 
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uh I'm not math head but I would recon that you didn't label something correct on your graph...20 what? perhaps he wants you to label everything, and I thought weight was in Newtons therefor you don't have to say weight * 9.8 m/s² because 9.8 m/s² is already included in the Newton measurement...yes? no?
 
According to your table:
weight(grams)*9.18m/s^2 | Scale reading (mm)
m1g = 114.26 | y1 4.7
m2g = 124.26 | y2 = 5.2
m3g = 134.26 | y3 = 5.9
m4g = 144.26 | y4 = 6.3
m5g = 154.26 | y5 = 6.7
m6g = 164.26 | y6 = 7.3
m7g = 174.26 | y7 = 7.8
m8g = 184.26 | y8 = 8.2

"m1g" is ALREADY multiplied by 9.81 (not "9.18") m/s^2. In order to convert that to Newtons, you only need to multiply by 0.001 to convert grams to kg. If that is correct, then m1g is 0.11426 Newtons and m8g is 0.18426. For those two values, y1= 0.0047 m and y8= 0.0082 m so the "slope" of your graph is (0.18426-0.11426)/(0.0082- 0.0047)= 20.
 
Coughlan, k is suppose to be 20N/m.

HallsofIvy, oh if that were only true, but those values did not include the multiplication of g. My masses were 114.26, 124.26, but were not already multiplied by g. Sorry, I should have written g next to them, but that could also be mistaken for grams (which they are in). I would convert to kg before multiplying with 9.8 anyhow, right? The m1g tells us to multiply m by g, ergo .11426kg*9.8m/s^2=1.12N.

Just in case I didn't clear it up, 9.8m/s^2 is not included in the measurement of 114.26, 124.26, etc...those are all masses in grams.

Any more suggestions?
Thank you.
Christina
 
Eh sorry about that...I'm fresh out of ideas...
 

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