Using LINEST in Excel to get the uncertainty in slope
Simple Harmonic motion lab for Physics 192
Use the LINEST function in EXCEL to calculate the uncertainty in slope. Highlight a 2X2
block of cells starting in F15. i.e, F15, F16, G15 and G16. Click up in the formula bar and
type
=LIN (the LINEST function should now appear) double click on it. For known y
values, highlight the values in the column where you have the y axis data, type a comma then
highlight the cells for the x values then type a comma then type 1,true and close the brackets.
If your y data (the extension of the spring) is in column B and your x data (the mass of the
hanging weights) is in column A then the formula should look like:
=LINEST(B1:B6,A1:A6,1,true). Don’t hit enter!! You must hold down ctrl-shift enter to get
the 4 values from the LINEST function. The values are the slope in the top left, the
uncertainty in slope in the bottom left, the y intercept in the top right and the uncertainty in
the y intercept in the bottom right. The uncertainties are absolute uncertainties. Calculate the
percent uncertainty in slope by dividing the absolute uncertainty by the slope and multiplying
by 100.
The second graph will have the period squared on the y axis and the mass of the x axis.
The slope of the extension versus mass graph is used to get k using the equation slope=g/k.
For the second graph of Period squared versus mass the spring constant is found using the
equation slope=4 Pi^2/k. The percent uncertainty in slope is the same as the percent
uncertainty in k for each graph. Do a consistency check between the 2 values of k found from
the two graphs.