For example, a car jack (Fig.Fig. 1 (a) Car jack to multiply force (b) Machines for increasing speed (bicycle) Another typical example is the bicycle (Fig.
![]() ![]() We can move more quickly on a bicycle than on foot. There are also other types of machines, which do not save energy or increase velocity, but are used to change directions of the applied forces conveniently. A machine is composed of different components called machine elements. Simple machines comprise a few machine elements and can operate individually, for example, bottle openers, scissors, pulleys and screw jacks. Machines composed of two or more simple machines are called compound machines. Examples are linkage, chain and sprocket of the bicycle, car engines etc. Fig. 2 Structure of a car Nowadays, people use more and more machine elements to increase the efficiency of machines. It is composed of many machine elements like lever, linkage, drive system, belts, bearings, clutch, gears, crank, cam, brake and ratchets. Furthermore, a screw jack can be used to raise the car for changing the tyres. To know the applications of technologies, we must understand the principles for the working of the machine elements. An effort is the force applied to the machines for lifting or carrying a load. Both are measured in Newton (N). Lever (b) Claw hammer Fig. Some examples of load-effort relationships. Mechanical Advantage If the applied force can raise a heavier load through a machine, the machine can save effort. Mechanical Advantage (MA) is the ratio of load to effort, and does not have any unit. Load Mechanical Advantage Effort OR MA E L If MA1, then LE, meaning that a heavier load can be moved by the effort. The larger the MA is, the smaller the effort to be applied to the machine will be. However, in practice, friction and the weight of the machine also affect the weight to be lifted as well as the Mechanical Advantage. What is the Mechanical Advantage of the block and tackle system as shown in the diagram below Solution: Load 1000 Mechanical Advantage 4 Effort 250 (c) Velocity Ratio Fig. Block and tackle system Refer to the block and tackle system in Fig. ![]() Velocity Ratio (VR) is the ratio of the distance moved by effort (d E ) to the distance moved by load (d L ). Velocity Ratio Distance moved by effort Distance moved by load OR VR d d E L For instance, in Fig. Therefore, the velocity ratio for the block and tackle system is: 4 m 4 1m The velocity ratio of machines is governed by their design. Solution: 5 m Velocity Ratio of the lever VR m (d) Work done The work done by a force on an object is equal to the force applied to such object multiplied by the distance moved along the direction of force by the object. Work done also refers to the energy required to move the object. Work done Force Distance moved OR W F s Example 3: A pulley system is used to lift a load.
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