Glass Plane 48" long, truck 1 lb. in
weight, friction counterpoised; formula
_P_ = 0·0208 × _h_".
+-----------+------+--------+-------------+-----------------------+
| Number of |Height|Observed| P. | Difference of the |
|Experiment.| of | power | Calculated |observed and calculated|
| |plane.| in lbs.|power in lbs.| powers |
+-----------+------+--------+-------------+-----------------------+
| 1 | 2" | 0·04 | 0·04 | 0·00 |
| 2 | 4" | 0·08 | 0·08 | 0·00 |
| 3 | 6" | 0·13 | 0·12 | -0·01 |
| 4 | 8" | 0·16 | 0·17 | +0·01 |
| 5 | 10" | 0·21 | 0·21 | 0·00 |
| 6 | 15" | 0·31 | 0·31 | 0·00 |
| 7 | 20" | 0·42 | 0·42 | 0·00 |
| 8 | 33" | 0·71 | 0·69 | -0·02 |
+-----------+------+--------+-------------+-----------------------+
Thus for example, in experiment 6, where the height B E is 15", it is
observed that the power necessary to draw the truck is 0·31 lb. The
truck is placed in the middle of the plane, and the power is adjusted
so as to be sufficient to draw the truck to the top with certainty; the
necessary power calculated by the formula is also 0·31 lbs., so that
the theory is verified.
264. The fifth column of the table shows the difference between the
observed and the calculated powers. The very slight differences, in no
case exceeding the fiftieth part of a pound, may be referred to the
inevitable errors of experiment.