CBSE Class 7 Science Advanced Physics Machines and Tools Long Answer Questions Set 01

Long Answer Questions

Question 1. Describe a wooden plough.
Answer:
A wooden plough is used by a farmer to plough the field. It has three main parts.
1. The main plough: a wooden piece slightly bent like the letter L. A handle is fixed at the top and a hole is made to hold the long pole. The lower end is sharply pointed and a metal blade is nailed to it, which helps the plough enter deep into the soil easily.
2. The long pole: a wooden pole about 2½ m long. One end is fixed to the 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 uses it to change the direction of ploughing and to control the depth of the soil ploughed.
The plough is pulled by a pair of bullocks.
In simple words: A bent wooden body with a metal blade, a long pole to the bullocks and a handle to steer it.

Teacher's Note:
1. Draw a neat labelled diagram of the plough.
2. Name the three parts and say what each does.

Question 2. Describe a hack-saw blade.
Answer:
A hack-saw blade is a thin, flat strip of steel with sharp teeth along one of its edges.
It has a small hole at each end, with which it is fixed tightly in the metal frame of the hack-saw. The frame carries a handle.
It is used to cut metal rods and pipes, and can also cut softer materials such as wood and plastics.
It can be removed and replaced when the teeth become blunt.
In simple words: A thin toothed steel strip, held in a frame, that cuts metal.

Teacher's Note:
1. Mention steel, teeth and the frame.
2. Draw the blade with the holes at its ends.

Question 3. Describe a seed-drill.
Answer:
A seed drill is a tool used to sow seeds.
1. Four or five small wooden ploughs with holes are fixed to a long horizontal wooden plank (or a metal tube).
2. The holes are joined to a funnel by plastic tubes.
3. Seeds are poured into the funnel; they pass through the tubes and fall into the shallow grooves made by the ploughs.
4. A long pole is fixed to the plank and tied to the yoke of the bullocks or to a tractor.
Advantages: the rows stay at a constant distance, the seeds fall at equal distances, and fertilizer or manure can be dropped near the roots.
In simple words: A plank with small ploughs and a funnel that drops seeds into grooves evenly.

Teacher's Note:
1. Include funnel, tubes, plank and ploughs in the answer.
2. End with the advantages.

Question 4. Write a short note on a wooden plough and an improvised plough.
Answer:
Wooden plough: it has a bent wooden main plough with a metal blade at its pointed end, a long pole joined to the bullocks' yoke and a handle to control the direction and depth.
Improvised plough: all its parts are made of iron or steel plates and strips.
1. It lasts much longer than a wooden plough.
2. It can plough the soil deeper.
3. It makes shallow grooves in which seeds are sown.
4. By changing the angle of its blades, the grooves can be covered after sowing.
In simple words: A wooden plough is made of wood with a metal tip, while an improvised plough is made fully of iron or steel and lasts longer.

Teacher's Note:
1. Compare the two kinds in your answer.
2. Material and life are the key differences.

Question 5. What are the advantages and disadvantages in using a vice?
Answer:
Vice is used to hold work pieces.
Advantages:
1. The work piece is gripped tightly in one position, so the worker's hands are free to work on it.
2. Small pieces of metal can be cut easily after being fixed between the jaws.
3. Threads can be made on pipes and surfaces can be smoothed while the piece is held.
Disadvantages:
1. Very thin and soft metals cannot be held in a vice.
2. A soft metal may change its shape and the jaws leave marks on its surface.
3. A work piece of bigger size cannot be held in the vice.
In simple words: A vice holds small, hard work pieces well, but it cannot hold thin, soft or big ones.

Teacher's Note:
1. Make two lists, one for each side.
2. Mention the free hands and the marks on soft metal.

Question 6. Komali found that most of the agricultural tools her father uses are made up of wood. Explain why it is so.
Answer:
1. Agricultural tools are always in contact with moisture, manure and so on, so metal parts would corrode (rust) more.
2. Agricultural tools are bigger than workshop tools and metal is heavy, but wood is much lighter than metal.
3. Therefore most of the parts of agricultural tools are made of wood, and metal is used only where hardness is needed, such as the blade.
In simple words: Wood is light and does not rust in wet soil, so farm tools are mostly wooden.

Teacher's Note:
1. Give two reasons: rusting and weight.
2. Remember that the blade is still made of metal.