Clarifications for lab report 4
1) Histograms
DO NOT USE EXCEL TO GRAPH THE HISTOGRAMS
Excel can do bar graphs, but they are not histograms. Draw the histograms by hand.
First choose a scale for your x axis (like you would for any other x axis)
Then choose a bin size; all bins must be the same width.
2) Averages
The averages you need to take are those of the "deltas", of the changes (in momentum or kinetic energy).
3) How to get the standard deviation algebraically is explained p.100 of your lab manual.
4) How much data must I use for each histogram?
At least the 15 lines on each page. Graph together the data corresponding to when the two carts had the same mass, and when the two carts had different masses.
5) What I explained in lab about the histograms and how to use them...
...in pictures! These are the snapshots of the board:
This is what each of your 4 histograms should look like, i.e. all that they should have on them (and it doesn't matter how high you draw the error bars, which are horizontal in this case):
Recall the definition of Delta:
This is what your error bars should look like or not, i.e. roughly how wide they should be compared to your histogram, so you can troubleshoot them. If yours look wrong, first check that you graphed them correctly, one standard deviation to the left of the average, and one standard deviation to the right; if that doesn't fix things, check your calculation of the standard deviation.
And finally, once you've got the error bars, this is how to tell whether your data says that the momentum / kinetic energy was conserved in the collision at stake (the vertical line represents the y axis, i.e. at x = 0):
