Size adapted for lifting weights up to 5 cwt.;
velocity ratio 12·5; mechanical efficiency 5;
useful effect 40 per cent.; calculated formula
_P_ = 5·8 + 0·185 _R_.
+-----------+---------+----------+----------+---------------+
| | | | P. | Difference |
| Number of | R. | Observed |Calculated|of the observed|
|Experiment.| Load | power | power | and calculated|
| | in lbs. | in lbs. | in lbs. | values. |
+-----------+---------+----------+----------+---------------+
| 1 | 56 | 15 | 16·2 | + 1·2 |
| 2 | 112 | 27 | 26·5 | - 0·5 |
| 3 | 168 | 40 | 36·9 | - 3·1 |
| 4 | 224 | 47 | 47·2 | + 0·2 |
| 5 | 280 | 56 | 57·6 | + 1·6 |
| 6 | 336 | 66 | 68·0 | + 2·0 |
| 7 | 392 | 78 | 78·3 | + 0·3 |
| 8 | 448 | 88 | 88·6 | + 0·6 |
| 9 | 504 | 100 | 99·0 | - 1·0 |
| 10 | 560 | 110 | 109·4 | - 0·6 |
+-----------+---------+----------+----------+---------------+
The fourth column shows the calculated values of the powers derived
from the formula. It will be seen by the last column that the formula
represents the experiments with but little error.
227. Since 60 per cent. of energy is consumed by friction, this
machine, like the differential pulley-block, sustains its load when
the chains are free. The differential pulley-block gives a mechanical
efficiency of 6, while the epicycloidal pulley-block has only a
mechanical efficiency of 5, and so far the former machine has the
advantage; on the other hand, that the epicycloidal pulley contains
but one block, and that its lifting chain has two hooks, are practical
conveniences strongly in its favour.
LECTURE VIII.
_THE LEVER._
The Lever of the First Order.—The Lever of the Second
Order.—The Shears.—The Lever of the Third Order.