N1 Engineering Science|The Easy Way! 29 b P A 120° 120° R C


Fig. 2.5 Bow’s notation (a) Space diagram


Fig. 2.5 Bow’s notation (a) Space diagram


(b) V(b) Vector diagram a


Te spaces between forces P, Q and R in the space diagram are lettered A, B and C, as shown in fig. 2.5 (a). For uniformity the lettering is done in a clockwise direction.


Force P, between space A and B, can be referred to as force AB, and Q and R as BC and CA respectively. Lower-case letters are used when lettering the vectors in the vector diagram, i.e. force P = ab, force Q = bc and force R = ca.


Section 1.4.2, page 7 should now be re-examined closely. 2.4 Lifting machines D


Liſting machines are mechanical devices designed to make work easier. Tese machines make it possible for a load (output force) larger that the applied effort (input force) to be raised. Crowbars, chain blocks, rope tackles and jacks are examples of liſting machines.


Definition 2.9 Lifting machine A liſting machine is a device enabling a load larger than the applied effort, to be raised.


2.4.1 Mechanical advantage (MA) D


A comparison of the load overcome, as opposed to the effort applied, will indicate the liſting advantage obtained by using a machine.


Definition 2.10 Mechanical advantage Mechanical advantage is the ratio of the load overcome as opposed to the corresponding effort applied.


i.e. MA= load effort ........................................................................................................... (2.2)


where MA=mechanical advantage (no units) load = load overcome in newtons (N) effort = applied effort in newtons (N)


ec or diagram Q B P R c Q b c a Shape diagramShape diagram


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