Chapter 10: Motions and Measurements of distances (Notes)
Posted on : 15-02-2019 Posted by : Admin

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Present day people travel to places very often and the means of transport has developed a lot. People travel by airplanes, trains, buses, cars, cycles, bullock carts etc. Man has also developed small wheeled vehicles that move on the soils on planet Mars. These vehicles collect samples from that planet and conduct experiments. These vehicles are sent to Mars with the help of a spacecraft.

 

Story of Transport

1. 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.
2. For transport along water routes, boats were used from ancient times. Initially, boats were simple logs of wood in with a hollow cavity.
3. Later, people learnt to put together different pieces of wood and give shapes to the boats. These shapes generally imitated the shapes of the animals living in water.
4. Invention of the wheel made a great change in modes of transport. Animals were used to pull vehicles that moved on wheels.
5. Until the beginning of the 19^th century, people still depended on animal power for transport.
6. The invention of steam engine introduced a new source of power. Railroads were made for steam engine driven carriages and wagons.
7. Later automobiles were invented. Motorized boats and ships were used as means of transport on water.
8. The early years of 1900 saw the development of airplanes. These were later improved to carry passengers and goods.
9. Electric trains, monorail, supersonic airplanes and spacecraft are some of the 20th century contributions   

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How far have you travelled? How wide is this desk?

It is important to know the distance a place, so that we can have an idea how to reach that place- by walk, take a bus or a train, a ship, an airplane or even a spacecraft!

Also sometimes, we need to know the length and width of the some objects.  It is much needed when we have to share half of our favorite chocolate with friend. People have been measuring distances even before the invention of standard scales.

There are so many occasions when we come across a need to measure lengths and distances.

• The tailor needs to measure the length of the cloth to know if it is enough to stitch a dress.
• A carpenter needs to measure the height and width of a cupboard to know how much wood he would need to make its door.
• The farmer needs to know the area of his land to estimate the amount of seed and water he would need for his crops.

 

Some measurements

Measurement means the comparison of an unknown quantity with some known quantity.  This known fixed quantity is called a unit. The result of a measurement is expressed in two parts. One part is a number. The other part is the unit of the measurement.

We can measure with the help of our body parts like hand span or foot length, but these measurements will be only approximations (not exact). This is because the size of body parts may be slightly different for different persons.

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Hence some standard measurements are needed which do not change from person to person. For example, in the above picture the pencil and clip are measured with the help of measuring scale. These measurements are standard and do not vary. Here pencil is measured to be 8 cm and the clip is measured to be 3 cm.

 

Standard units of measurements

In ancient times, the length of a foot, the width of a finger, and the distance of a step were commonly used as different units of measurements.

The people of the Indus valley civilization must have used very good measurements of length because we see evidence in excavations of perfectly geometrical constructions.

A cubit as the length from the elbow to the finger tips was used in ancient Egypt and was also accepted as a unit of length in other parts of the world.

People also used the "foot" as a unit of length in different parts of the world. The length of the foot used varied slightly from region to region.

People measured a yard of cloth by the distance between the end of the outstretched arm and their chin.

In ancient India, small length measurements used were an angul (finger) or a mutthi (fist). Even today, we can see flower sellers using their forearm as a unit of length for garlands in many towns of India. Many such body parts continue to be in use as unit of length, when convenient.

Because the size of body parts may be slightly different for different persons French people created standard units of measurements in the year1790. This system ofstandard units for measurement is called as metric system.

For the sake of uniformity, scientists all over the world have accepted a set of standard units of measurement. The system of units now used is known as the International System of Units (SI units). The SI unit of length is a metre.

Each metre (m) is divided into 100 equal divisions, called centimetre (cm). Each centimetre has ten equal divisions, called millimetre (mm). Thus,

1 m = 100 cm

1 cm = 10 mm

For measuring large distances, metre is not a convenient unit. We define a larger unit of length. It is called kilometre (km).

1 km = 1000 m

 

Correct measurement of length

In our daily life we use various types of measuring devices. We use a metre scale for measuring length. A tailor uses a measuring tape, whereas a cloth merchant uses a metre rod. For small measurements, such as the length of your pencil, you can use a 15 cm scale from your geometry box.

In taking measurement of a length, we need to take care of the following:

1. Place the scale in contact with the object along its length as shown.
2. In some scales, the ends may be broken. You may not be able to see the zero mark clearly. In such cases, you should avoid taking measurements from the zero mark of the scale. You can use any other full mark of the scale. Then you must subtract the reading of this mark from the reading at the other end.
3. Correct position of the eye is also important for taking measurement. Your eye must be exactly in front of the point where the measurement is to be taken. Position 'B' is the correct position of the eye. Note that from position 'B', the reading is 7.5 cm. From positions 'A' and 'C', the readings may be different.

 

Measuring of length of a curved line

We cannot measure the length of a curved line directly by using a metre scale. Hence we have to use a thread to measure the length of a curved line.

1. Use a thread to measure the length of the curved line AB.
2. Put a knot on the thread near one of its ends. Place this knot on the point A.
3. Now, place a small portion of the thread along the line, keeping it stretched using your fingers and thumb.
4. Hold the thread at this end point with one hand.
5. Using the other hand, stretch a little more portion of the thread along the curved line.
6. Go on repeating this process till the other end B of the curved line is reached.
7. Make a mark on the thread where it touches the end B.
8. Now stretch the thread along a metre scale. Measure the length between the knot in the beginning and the final mark on the thread.

This gives the length of the curved line AB. We see that we need a lot of care to ensure that we are measuring distances and lengths correctly. And, we need some standard units and devices with which we measure these distances and can convey our results to others.

 

Moving things around

When we observe things around us, we can notice that few of them move and few do not move. The bird is not at the same place after some time, while the table is at the same place. On this basis you may have decided whether an object is at rest or in motion.

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