. Laboratory lessons in general science . elative valuesof Pand W? Make a drawing to represent the lever in some one ofthese positions, and label it 2d Class Lever. 3. Arrange the lever now so that the pull of the balance(P) is upward, and between W and F. State what is foundtrue under these conditions (a) of the moments of P and W;(6) of the relative values of P and W. Make a drawing torepresent a 3d Class Lever, putting upon it the valuesfound in some one of the cases for P and W, and for Pd andWd. PULLEYS (a) With the Cord Attached to the Fixed Pulley It is desirable to have a pair of tripl
. Laboratory lessons in general science . elative valuesof Pand W? Make a drawing to represent the lever in some one ofthese positions, and label it 2d Class Lever. 3. Arrange the lever now so that the pull of the balance(P) is upward, and between W and F. State what is foundtrue under these conditions (a) of the moments of P and W;(6) of the relative values of P and W. Make a drawing torepresent a 3d Class Lever, putting upon it the valuesfound in some one of the cases for P and W, and for Pd andWd. PULLEYS (a) With the Cord Attached to the Fixed Pulley It is desirable to have a pair of triple-tandem pulleys as rep-resented in the cut, and a spring balance graduated both in grams andin ounces. A length of stout, smooth cord with loops at its ends iseasily provided. 164 LABORATORY LESSONS IN GENERAL SCIENCE 1. Make two freehand drawings on your paper similarto the cut, showing in the first one movable pulley in use,and in the second two movable pulleys. In all cases repre-sent one end of the cord attached to the fixed Fig. 73. — Diagram of pulleys. 2. Let the teacher fit up pulleys in turn representingthese same conditions, and determine by use of the springbalance in each case (a) the value of the resistance overcome(, the weight of movable pulley and its attached body x); 1 Any friction, or resistance other than gravity, is disregarded here. WORK AND MACHINES 165 (b) the effort put forth (pull exerted) to lift the on your drawings the values found by the teacher,marking the resistance as W (weight), and the effort as P(power). Be sure to verify the correctness of your drawings byreference each time to the pulley arrangement as set up bythe teacher. 3. Let the teacher take the readings of the spring balancefor the value of P (a) when pulling down over the last of thefixed pulleys; (b) when lifting up, and not using this lastfixed pulley. Infer (a) the only purpose of this fixed pulley;(6) whether the section of cord for pulling downward s
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