10 Motion and Measurement of Distances T

1 10 Motion andMeasurement of DistancesThere was a general discussionamong the children in Paheli andBoojho's class about the placesthey had visited during the summervacations. Someone had gone to theirnative village by a train, then a bus, andfinally a bullock cart. One student hadtravelled by an aeroplane. Another spentmany days of his holidays going onfishing trips in his uncle's teacher then asked them to readnewspaper articles that mentionedabout small wheeled vehicles that movedon the soil of Mars and conductedexperiments. These vehicles were takenby spacecraft all the way to Mars!Meanwhile, Paheli had been readingstories about ancient India and wantedto know how people travelled from oneplace to another in earlier STORY OF TRANSPORTLong ago people did not have any meansof transport.

2 They used to move only onfoot and carry goods on their back. Lateron they began to use animals transport through water, routes,boats were used from ancient times. Tobegin with, boats were simple logs ofwood in which a hollow cavity could bemade. Later, people learnt to puttogether different pieces of wood andgive shapes to the boats. These shapesimitated the shapes of the animals livingin water. Recall our discussions of thisstreamlined shape of fish in Chapters8 and of the wheel made a greatchange in modes of transport. Thedesign of the wheel was improved overthousands of years. Animals were usedto pull carts that moved on the beginning of the 19thcentury, people still depended onanimals, boats and ships to transportthem from place to place.

3 The inventionof steam engine led to the developmentof new means of transport. Railroadswere made for steam engine drivencarriages and wagons. Later cameFig Some means of transportation2022-2396 SCIENCE automobiles such as motor cars, trucksand buses. Motorised boats and ships wereused as means of transport on water. Theearly years of 1900 saw the developmentof aeroplanes. These were later improvedto carry passengers and goods. Electrictrains, monorail, supersonic aeroplanesand spacecraft are some of thecontributions of the 20th shows some of the differentmodes of transport. Place them in thecorrect order from the earliest modesof transport to the most there any of the early modes oftransport that are not in use today?

4 WIDE IS THIS DESK?How did people know how far they havetravelled?How will you know whether you canwalk all the way to your school or whetheryou will need to take a bus or a rickshawto reach your school? When you need topurchase something, is it possible for youto walk to the market? How will you knowthe answers to these questions?It is often important to know how fara place is, so that we can have an ideahow we are going to reach that place walk, take a bus or a train, a ship, anaeroplane or even a spacecraft!Sometimes, there are objects whoselength or width we need to Paheli and Boojho's classroom,there are large desks which are to beshared by two students.

5 Paheli andBoojho share one desk, but, frequentlyend up objecting that the other is usinga larger share of the the teacher's suggestion, theydecided to measure the length of thedesk, make a mark exactly in the middleof it and draw a line to separate the twohalves of the Paheli and Boojho are very fondof playing gilli danda with their brought a set of gilli and dandawith is how they tried to measurethe length of the desk using the dandaand the gilli (Fig. ).The desk seems to be having alength equal to two danda lengths andtwo lengths of the gilli. Drawing a linein the middle of the desk leaves eachof them happy with a half of the deskequal to a danda and a gilli in a few days, the marked line getswiped out.

6 Boojho now has a new setof gilli and danda as he lost his oldone. Here is how, the length of thedesk seems to measure using the gilliand danda (Fig. ).Fig. Measuring the length of the desk witha different set of gilli and dandaFig. Measuring the length of a desk withgilli and danda2022-2397 Motion AND Measurement OF DISTANCESH ello! Now, when measured with thenew set of gilli and danda, the desklength seems to be about two dandalengths, one gilli length with a smalllength still left out. This is less than onegilli length. Now what?What would you suggest Paheli andBoojho do, to measure the length of thewhole desk? Can they use a cricketwicket and bails to measure the lengthor do you think that this might createthe similar problem?

7 One thing they could do is to take asmall length of string and mark two pointson it. This will be a string length. Theycan measure the width of the desk instring lengths (Fig. ). How can theyuse the string to measure Distances lessthan the length of a string? They can foldthe string and mark it into 12, 14 and 18'string lengths'. Now, perhaps Paheli andBoojho can measure the exact length ofthe desk using the would say that they should usethe scale in their geometry box and solvetheir problem? Yes, Of course!Boojho has been reading about theway people used to measure distancesbefore such standard scales were madeand he has been trying to follow differentmethods of measuring are so many occasions when wecome across a need to measure lengthsand Distances .

8 The tailor needs to measurethe length of the cloth to know if it isenough to stitch a kurta. A carpenterneeds to measure the height and widthof a cupboard to know how much woodhe would need to make its door. Thefarmer needs to know the length andbreadth or the area of his land to knowhow much seed he can sow and howmuch water would be needed for his , you are asked how tall youare? You want to tell the length of astraight line from the top of your headto the heel of your long is this room?How wide is this desk?How far is it from Delhi to Lucknow?How far away is the Moon from theEarth?All these questions have one thingin common.

9 They all concern distancebetween two places. The two places maybe close enough, like the two ends of atable or they may be far apart, likeJammu and us do a few measurements to seewhat exactly we need to do, when wemeasure Distances or SOME MEASUREMENTSA ctivity 1 Work in groups and each of you do thisactivity one by one. Using your foot as aFig. Measuring the length of the desk withstring lengths2022-2398 SCIENCE unit of length, measure the length andbreadth of the classroom. It is possiblethat while measuring these you may findsome part remains to be measured as itis smaller than your foot. Use a stringto measure the length of a part of yourfoot as you did before.

10 Record yourobservations in Table Measuring length andbreadth of classroomfoemaNtnedutsehtfohtgneLmoorssa lcehtfohtdiWmoorssalcActivity 2 Work in a group and each of you useyour handspan as a unit to measurethe width of a table or a desk in theclassroom (Fig. ).with some known quantity. This knownfixed quantity is called a unit. The resultof a Measurement is expressed in twoparts. One part is a number. The otherpart is the unit of the Measurement . Forexample, if in Activity 1, the length ofthe room is found to be 12 lengths ofyour foot, then 12 is the number and'foot length' is the unit selected for , study all the measurementsrecorded in Table and Are allthe measurements for the room usingeverybody's foot, equal?