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Motion and Measurement of Distances
There was a general discussion among the children in Paheli and Boojho's class about the places they had visited during the summer vacations. Someone had gone to their native village by a train, then a bus, and finally a bullock cart. One student had travelled by an aeroplane. Another spent many days of his holidays going on fishing trips in his uncle's boat. The teacher then asked them to read newspaper articles that mentioned about small wheeled vehicles that move on the soil of Mars and conductedexperiments. These vehicles were taken by spacecraft all the way to Mars! Meanwhile, Paheli had been reading stories about ancient India and wanted to know how people travelled from one place to another in earlier times.
10.1 STORY OF TRANSPORT
Long ago people did not have any means of transport. They used to move only on foot and carry goods either on their back or using animals. For transport along water routes, boats were used from ancient times. To begin with, boats were simple logs of wood in which a hollow cavity could be made. Later, people learnt to put together different pieces of wood and give shapes to the boats. These shapes imitated the shapes of the animals living in water. Recall our discussions of this streamlined shape of fish . Invention of the wheel made a great change in modes of transport. The design of the wheel was improved over thousands of years. Animals were used to pull vehicles that moved on wheels. Until the beginning of the 19th century, people still depended on animal power to transport them from place to place. The invention of steam engine introduced a new source of power. Railroads were made for steam engine driven carriages and wagons.
10.1 STORY OF TRANSPORT
Long ago people did not have any means of transport. They used to move only on foot and carry goods either on their back or using animals. For transport along water routes, boats were used from ancient times. To begin with, boats were simple logs of wood in which a hollow cavity could be made. Later, people learnt to put together different pieces of wood and give shapes to the boats. These shapes Later came automobiles. Motorised boats and ships were used as means of transport on water. The early years of 1900 saw the development of aeroplanes. These were later improved to carry passengers and goods. Electric trains, monorail, supersonic aeroplanes and spacecraft are some of the 20th century contributions. Fig. 10.1 shows some of the different modes of transport. Place them in the correct order — from the earliest modes of transport to the most recent. Are there any of the early modes of transport that are not in use today?
10.2 HOW FAR HAVE YOU TRAVELLED? HOW WIDE IS THIS DESK?
How did people know how far they have travelled? How will you know whether you can walk all the way to your school or whether you will need to take a bus or a rickshaw to reach your school? When you need to purchase something, is it possible for you to walk to the market? How will you know the answers to these questions? It is often important to know how far a place is, so that we can have an idea how we are going to reach that place — walk, take a bus or a train, a ship, an aeroplane or even a spacecraft! Sometimes, there are objects whose length or width we need to know In Paheli and Boojho's classroom, there are large desks which are to be shared by two students. Paheli and Boojho share one desk, but, frequently end up fighting that the other is using a larger share of the desk. Hello! Now, when measured with the new set of gilli and danda, the desk length seems to be about two danda lengths, one gilli length with a small length still left out. This is less than one gilli length. Now what? What would you suggest Paheli and Boojho do, to measure the length of the whole desk? Can they use a cricket wicket and bails to measure the length or do you think that this might create the similar problem? One thing they could do is to take a small length of string and mark two points on it. This will be a string length. They can measure the width of the desk in string lengths (Fig. 10.4). How can they use the string to measure distances less than the length of a string?
1. Give two examples each, of modes of transport used on land, water and air.
2. Fill in the blanks:
(i) One metre is ______________ cm.
(ii) Five kilometre is ______________ m.
(iii)Motion of a child on a swing is ______________.
(iv) Motion of the needle of a sewing machine is ______________.
(v) Motion of wheel of a bicycle is______________.
3. Why can a pace or a footstep not be used as a standard unit of length?
4. Arrange the following lengths in their increasing magnitude: 1 metre, 1 centimetre, 1 kilometre,1 millimetre.
5. The height of a person is 1.65 m. Express it into cm and mm.
6. The distance between Radha's home and her school is 3250 m. Express this distance into km.
7. While measuring the length of a knitting needle, the reading of the scale at one end is 3.0 cm and at the other end is 33.1 cm. What is the length of the needle?
8. Write the similarities and differences between the motion of a bicycle and a ceiling fan that has been switched on.
9. Why could you not use an elastic measuring tape to measure distance? What would be some of the problems you would meet in telling someone about a distance you measured with an elastic tape?
10. Give two examples of periodic motion
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