Question

# Answer the following questions : (a) What are simple machines? Give examples. (b) What are the advantages of using a machine? (c) What is meant by a pulley? (d) What can you use as an inclined plane? (e) What is meant by a lever? (f) What is meant by a complex machine? Give an example. (g) How many types of levers are there? On what basis are they classified? (h) What should we do to take care of machines?

Solution

## (a) A device with a simple structure, which is used to do simple work, is called a simple machine. The characteristic feature of simple machines is that they do not convert energy from one form to another. For example, seesaw, crowbar, nutcracker, pulley and tongs. (b) Machines are used to reduce the labour and time required for some work. (c) A pulley is a simple machine. It has a wheel with a groove on its rim. A pulley system is used for lifting heavy loads easily. (d) A sloping plank of wood or a slope constructed from masonry or a strong steel plate can be used as an inclined plane.  (e) A lever is a simple machine. It consists of a rigid rod which is capable of turning around a pivot or a support. It is also called a fulcrum. There are three types of levers according to the position of the applied force, the load and the fulcrum.  (f) A machine that is made of more than one simple machine is called a complex machine. For example, a bicycle and a crusher. (g) Levers are classified into three types depending upon the positions of load, fulcrum and effort. Lever of first order When the fulcrum is situated between the load and the effort, we call it a lever of the first order. For example, a beam balance, a crowbar and a seesaw.     Lever of second order When the fulcrum and the effort are situated at the two opposite ends of the lever and a load is placed in between them, we call it a lever of the second order. For example, a nutcracker or a wheelbarrow.   Lever of the third order When the fulcrum and the load is situated at the opposite ends of the lever and an effort is applied somewhere between them, we call it a lever of the third order. For example, a pair of tongs or a fishing rod.   (h) We must take care of machines to minimize their wear and tear by: • Keeping them away from dust and moisture • Lubricating them properly • Painting iron parts of the machinesScienceScience and TechnologyStandard VI

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