In a test of air drag, a sphere is launched
at various speeds (x, in m/s) and
the resulting drag force (y, in N)
is determined. The force measurements
have an accuracy of 5%.
Lord Rayleigh asserted that there is a power-law relationship between
x and y, with exponent near
2.
- Fit this data to a power law relationship.
- Consider Rayleigh's scientific claim of an power law.
Does this evidence (data) confirm or contradict this claim? Support
your answer quantitatively.
- Properly report (sigfigs, error, units) the exponent for
the best-fit power law.
The expected relationship between the drag-force, F,
and speed, v, is:
F = CD (0.5 ρ π R2) v2
where CD is the drag coefficient and the quantity in parentheses has the value:
(0.5 ρ π R2) = 0.03 kg/m
So:
CD = A / (0.03 kg/m)
Do an additional fit with the exponent held fixed at 2.
- Properly report (sigfigs, error, units) the A parameter for this second fit.
- Use a spreadsheet to calculate the drag coefficient from A, and properly report
(sigfigs, error, units) the value.
- Self-document the spreadsheet and turn in a hardcopy of the page.
- Make a hardcopy plot of the data with best-fit curve. Make an additional hardcopy plot
with scales chosen so as to linearize the curve.
- Turn in fit reports from both fits (i.e., steps 3 and 4).
X (m/s) | Y (N)
|
---|
1.53 | 3.13E-2
|
2.4 | 7.67E-2
|
2.9 | 0.107
|
5.2 | 0.401
|
5.5 | 0.411
|
12.7 | 2.17
|
22 | 6.19
|
27 | 9.81
|
49 | 28.8
|
79 | 82.6
|