Friction of pine upon pine; the mean values of the
friction given in Table II. (corrected for the
friction of the pulley) compared with the formula
_F_ = 0·288 _R_
+-----------+----------+---------+----------+-------------+
| | | | |Discrepancies|
| Number of | R. |Corrected| F. | between the |
|Experiment.|Total load| mean |Calculated| observed and|
| |on slide |value of |value of | calculated |
| | in lbs. |friction.| friction.| frictions. |
+-----------+----------+---------+----------+-------------+
| 1 | 14 | 4·7 | 4·0 | -0·7 |
| 2 | 28 | 8·2 | 8·1 | -0·1 |
| 3 | 42 | 12·2 | 12·1 | -0·1 |
| 4 | 56 | 15·8 | 16·1 | +0·3 |
+-----------+----------+---------+----------+-------------+
141. But we can replace the common law of friction by the more accurate
law of Art. 137, and the formula computed so as to best harmonise
the experiments up to 56 lbs., disregarding the higher loads, is
_F_ = 0·9 + 0·266 _R_. This formula is obtained by the method referred
to in Art. 137. We find that it represents the experiments better
than that used in Table V. Between the limits named, this formula is
also more accurate than that of Table IV. It is compared with the
experiments in Table VI., and it will be noticed that it represents
them with great precision, as no discrepancy exceeds 0·1.