CBSE Class 7 Science Advanced Physics Machines and Tools Notes Set 01

Machines and Tools

Introduction

Think of a carpenter at work. A screw driver is needed to drive a screw in and the same screw driver is needed to take it out again. Without it the job would be very hard. For different jobs he picks different tools such as knives, scissors, hammers and tin-cutters. A tool lets us finish a job with less effort, but it never reduces the amount of work that has to be done.

The Hammer

A hammer has a heavy metal head fixed on a wooden handle. It is mainly used to drive nails in or pull them out, and also to break stones and to flatten metal. Hammers are of two kinds.

1. An ordinary hammer
2. A hammer with a forked (claw) part

An ordinary hammer can only drive nails in. A hammer with a fork can drive nails in and can also pull them out, because the forked side grips the nail.

Fig. 7.1 Ordinary hammer

Fig. 7.2 Hammer with a forked part

The Dividers

Dividers are used to measure distances, to mark off equal lengths and to draw circles on wood and plastic. A pair of dividers is made of two iron strips of the same length joined at a pivot (fulcrum), about which they can be opened or closed. The free ends of both strips are pointed.

Fig. 7.3 Dividers

The Hack-saw and Hack-saw Blade

A hack-saw is used mainly to cut metal rods. Its steel blade has sharp teeth along one edge and is held tight in a metal frame that carries a handle. The same saw can also cut softer materials such as wood and plastic.

Fig. 7.4 (a) Hack-saw; (b) Hack-saw blade

The Vice

When a metal plate or rod has to be cut, it is hard to hold it with one hand and cut with the other. A vice grips the piece firmly so that both hands are free. It is clamped to the edge of a table with a screw. A vice has two jaws: one is fixed to the table and the other can be moved by a screw. The work piece is placed between the jaws.

1. Turning the screw clockwise brings the movable jaw closer to the fixed jaw, so the vice tightens.
2. Turning the screw anti-clockwise moves the movable jaw away, so the vice loosens.

Fig. 7.5 Vice

Metal plates and pipes are cut while they are gripped in a vice. Threads can be cut on a pipe held between its jaws, and a held surface can be smoothed (filed).

The Tin-cutter

A tin-cutter cuts thin metal sheets and plates. It looks like a pair of scissors, but a spring is fixed between the handle of one blade and the other blade. The energy stored in the spring helps to open the blades again, which saves effort.

Fig. 7.6 Tin cutter

The Multipurpose Tool

A multipurpose tool can do many kinds of jobs. It has a collet, which grips whichever tool is fitted into it, so the job decides which tool is fixed. The tools that can be fitted are:

1. a carpenter's hand saw, to cut wood
2. a screw driver, to tighten or loosen screws
3. a poker, to make holes in metal rods or strips
4. a drill bit, to drill holes in wooden planks
5. a file, to smooth the surfaces of metal and wooden articles
6. a chisel, to cut grooves in wooden planks

Fig. 7.7 Multipurpose tool

Tools Used in Agriculture

Farmers use another group of tools for their field work. They are described below.

The Wooden Plough

A farmer uses a wooden plough to turn over the soil of his field. It has three main parts.

1. The main plough: a wooden piece bent slightly like the letter L. Near its upper end there is a place to fix the handle and a hole for the long pole. The lower end is sharpened and a metal blade is nailed on to it, which helps the plough cut deep into the soil easily.
2. The long pole: a wooden pole about \( 2\frac{1}{2} \) m long. One end is fixed in the main plough and the other end is tied to the yoke of the bullocks.
3. The handle: fixed at the end opposite to the pointed end. The farmer holds it to turn the plough in the required direction and to control how deep the soil is ploughed.

The Improvised Plough

Every part of an improvised plough is made of iron or steel plates and strips. It lasts much longer than a wooden plough and can dig deeper. It can also make shallow grooves in the soil in which seeds are sown. By changing the angle of its blades, the same grooves can be closed again after the seeds have been sown.

Fig. 7.8 Improvised plough

The Wooden Plank

A wooden plank is made of three straight horizontal planks joined by two upright planks, which are held with metal strips. Clods of hard mud on the surface stop seeds from sprouting, so the plants do not grow well. The plank is tied to the yoke of two bullocks and dragged over the field to crush these clods.

Fig. 7.9 Wooden plank

The Leveller

A leveller makes the surface of the soil flat. It has a heavy wooden frame with a metal strip fixed along its lower edge, a handle at the upper end and two rings on the frame. It is pulled by bullocks or a tractor while the farmer holds the handle.

Fig. 7.10 Leveller

The Seed Drill

A seed drill sows seeds. Four or five small wooden ploughs with holes are fixed to a horizontal wooden plank (or a metal tube). Plastic tubes join the holes to a funnel. The farmer pours seeds into the funnel; they slide down the tubes and fall into the grooves made by the ploughs.

1. The gap between two rows of seeds stays the same.
2. The seeds fall at equal distances from each other.
3. Fertilizer or manure can be dropped close to the roots of the plants in the same way.

Fig. 7.11 Seed-Drill

The Harrow

A harrow has many sharp metal nails fixed in a long horizontal wooden strip. Another wooden plank with a handle is attached to this strip. It pulls out weeds from the field and also levels wet soil before young plants are transplanted.

Fig. 7.12 Harrow

A pair of bullocks or a tractor can pull all of these agricultural tools.

The Maintenance of Tools

Every tool, including the farm tools, needs proper care. Wooden tools should be cleaned after each use. Metal tools should be oiled or greased from time to time so that they do not rust.

Points to Remember

1. Tools let us do a job with less effort.
2. A divider measures lengths and draws circles on soft material.
3. A hack-saw cuts metal rods.
4. Different tools can be fitted in the collet of a multipurpose tool.
5. A wooden plough has three parts: the main plough, the long pole and the handle.
6. A wooden plank breaks hard clods of mud.
7. A leveller levels the soil surface.
8. A seed drill sows seeds.
9. A harrow removes weeds from the field.