Smooth plane of pine 72" × 11"; angle of
inclination 17°·2; slide of pine, grain
crosswise; slide started; formula
_P_ = 0·571 _R_.
+-----------+----------+----------+----------+--------------+
| | R. |Power in | P. |Difference of |
|Number of |Total load|lbs. which|Calculated| the observed |
|Experiment.| on slide |just draws| value of |and calculated|
| | in lbs. | up slide.|the power.| powers. |
+-----------+----------+----------+----------+--------------+
| 1 | 7 | 4·6 | 4·0 | -0·6 |
| 2 | 14 | 8·3 | 8·0 | -0·3 |
| 3 | 21 | 12·3 | 12·0 | -0·3 |
| 4 | 28 | 16·5 | 16·0 | -0·5 |
| 5 | 35 | 20·0 | 20·0 | 0·0 |
| 6 | 42 | 24·2 | 24·0 | -0·2 |
| 7 | 49 | 28·0 | 28·0 | 0·0 |
| 8 | 56 | 31·8 | 32·0 | +0·2 |
+-----------+----------+----------+----------+--------------+
271. Thus for example, in experiment 6, a load of 42 lbs. was raised
by a force of 24·2 lbs., while the calculated value is 24·0 lbs.; the
difference, 0·2 lbs., is shown in the last column.
272. The calculated values are found to agree tolerably well with the
observed values, but the presence of the large differences in No. 1 and
No. 4 leads us to inquire whether by employing the more accurate law of
friction (Art. 141) a better result may not be obtained.
In Table VI. we have shown that the friction for weights not exceeding
56 lbs. is expressed by the formula _F_ = 0·9 + 0·266 × pressure, but
the pressure is in this case = 0·955 _R_, and hence the friction is