Methods used to facilitate work

You have already learnt that machines are used to make tasks easier. Some examples of simple machines are lever, inclined plane, pulley and wheel and axel.More over, you know that energy could be transmitted using endless chains, cog wheels, rods, fluids and air. Complex machines could be assembled using simple
machines. Man uses machines and mechanical devices to fulfil his needs in day today life. Now, let us consider some machines and mechanical devices used by man in the fields of building construction, repairing motor vehicles and agriculture.

Machines used in building construction

You may have seen that machines are used for levelling the sites, digging pits and ditches, piling, masonry and carpentry work in the field of construction

Some machines used in construction sites

The table you prepared for the above assignment may contain mammoty, pickaxe,crow-bar, wheel barrow, claw-hammer, pulley,hand drill, electric drill and chisel as machines. There may be bulldozer, tractor, backhoe, crane, pile driver and concrete mixer machines in your table. Let us now, consider about a few of those machines, or devices.

1. Bulldozer
Bulldozer is used to fell down trees and boulders, to load soil, to push boulders and soil and to level the sites. See the fig  below.

A bulldozer

A tree or a boulder could be fell down by raising the blade of the bulldozer and pushing with it. Land could be bladed and

levelled using the blade of the dozer. To move various parts,
there are joints made in such a way like the elbow joint of man (E.g 3:2.3 and 3.2.4) There should be relative motions of the
steel bars of a bulldozer for raising and lowering of various things. Those steel bars are riveted to each other using bolts. Such a joint is shown in fig 3.2.3. Suppose the load at C is to
be raised. For this, the bar AC should be moved away from the bar AB. In other words, the angle BAC should be increased. To do this, the length of the jack fitted to the points D and E should be increased. This is done by pumping oil into
the cylinder of the jack. The operator of the bulldozer does this by pulling a lever. Here, this machine acts as a lever of 3rd order, just like the elbow joint of man (Fig 3.2.4). Force is
supplied to the hydrolic jack, which acts as the effort, by transmission of fluid.

2. Backhoe machine                          

Backhoe machine is used to cut ditches for foundations and to dig holes for piles. For this purpose, there is a narrow claw - like cutting tool at the end of a long arm. The movement of this part is done in the same way like the blade of bulldozer.There are two endless broad iron chains, instead of tyres, in most of the backhoes. These chains increase the grip between the machine and the ground. Hence it increases the friction. More over, the wide surface area of the chain decreases the pressure on the ground. Therefore, the machine does not sink into the soil.

3. Pile driver

When storied buildings are constructed, large concrete piles are sunk into the soil to hold the weight of the building. In unstable soils, these piles are sunk to reach the bed rock. To drive the pile into the soil, heavy load is lifted by a crane, and dropped on to the pile head under gravity. This heavy load is known as pile driver.

There are pulleys and pulley systems in the crane for the lifting of pile driver. If the pressure excerted by the pile on the soil is increased, it will easily sink into the soil. For this purpose, the bottom of the pile is pointed. The function of this pointed part is similar to an inclined plane. A large amount of kinetic energy is released due to the heavy mass of the pile driver and the high velocity of the falling pile driver. This kinetic energy is exerted on to the pile head. As a result, pile sink into the soil (Fig 3.2.7).This process is very much similar to sink a wedge in soil. (The steel cap on the pile head prevents damaging the pile)