PASCO SE-9076 Constant Velocity Tubes - Manual (Page 10)

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Constant Velocity Tubes 012–06697B
4. On the same graph, plot this additional data:
150 ml — 2,500 g and 100 ml — 1,600 g
5. Looking at your graph, what volume would you suggest be used next?
________________
6. Now plot this data pair: 200 ml — 1,300 g
➤ Plotting data on a graph helps reveal mistakes. If the graph is
made as the experiment is being done, the mistake can be corrected.
Later, it may be difficult or impossible to reconstruct the experiment
and correct the error.
7. Which of the data points on your graph represents a mistake? __________________
➤ It is not wise to immediately discard data that “looks wrong”.
Many important new discoveries in science “looked wrong” at first.
In this case, however, a simple mistake was made: the “1” and the
“3” in the last mass reading were transposed. The data pair should
have been: 200 ml — 3,100 g.
8. Correct the mistake noted.
9. By now a pattern should be clear. To make the pattern more visible, draw a best-fit
line (the line that most closely follows the pattern revealed by the data points).
Since the pattern seems to be straight, it is appropriate to use a straight edge to draw
the line. (A transparent plastic straight edge is particularly useful for this purpose.)
Extend the line all the way to the vertical axis.
➤ You may find that the points don’t quite fit on the line. This is
because all of our data include uncertainty. The uncertainty is due
to imperfections in the measuring tools, our inability to read these
tools perfectly, and perhaps the fact that other variables have varied
despite our attempts to keep them constant. The odds are that some
of the points are too high, and some are too low. Even though the
uncertainty in the data makes the locations of the data points slightly
in error, we can discover the pattern that represents the true
relationship between mass and volume. We assume that the truth is
that the pattern is a straight line, and that the points miss the line due
to errors.
➤ Computer programs, including built-in programs in some calcu-
lators and Science Workshop® can also draw a best-fit line. The
process is called curve-fitting. If we decide in advance that a straight
line is the appropriate pattern, the process is called linear
regression.