Measurement Of Length – Standard Units and Instruments

When we measure the distance between any two points in terms of width, thickness, depth, and height, we measure length. Standard International (SI) unit for measurement of length is ‘meter’. The standard instruments used nowadays to measure a length are – ruler, meter scale, measuring tape, vernier caliper, and screw gauge. However, ancient people used instruments like – hand span, foot, arm length, ropes, sticks, etc. to measure length.

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Definition of length

Length is the measure of distance between any two points.

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Definition for Measurement of Length

Measurement of length is the process of measuring the distance between any two points in term of width, thickness, depth, and height.

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Continue>>Measurement of length

Importance of Measurement of Length

To understand the importance of measurement consider this – if you have two pencils and want to know which one of the two is longer, then you can easily find it out by placing both of them side by side. However, there are situations when you cannot move objects and place them side by side. Take the example of your’s teacher table and the dining table at your home. If you want to know which one of the two is longer, you just cannot carry the teacher’s table to your house or your dining table to the school. However, if you measure the length of the teacher’s table by the span of your palm and compare it with the length of the dining table by the span of your palm, you will easily find out which one of the two tables is longer.

Now think what did you did to find the answer. You did not move any of the tables. Instead, you moved from the school to the dining room. To measure the length, you used the third object or an instrument, that is your palm. Similarly, various other instruments used for measuring length are a ruler, meter scale, measuring tape, vernier caliper, and screw gauge.

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STANDARD UNIT (SI) FOR MEASUREMENT OF LENGTH

In the above example, you used the span of your palm or hand to measure length. Although this method to measure length may be simple, but it is not accurate. For example, if you and your father both measure the length of the sofa in your drawing room with a hand span as an instrument. The number of hand span measured by you on the same sofa will be more than that of your father’s. This is because your hand span is smaller than your father’s.

So, to maintain uniformity, people all over the world use meter as the standard unit for length. The meter scale is used as the standard instrument to measure length. To ensure that it is the same meter used everywhere, the standard meter was defined by scientists as below:

Definitions of the meter (1798) –

One meter is one ten-millionth (1/10,000,000) of the distance from the Equator to the North pole along the longitude passing through the Paris in France.

Definitions of the meter (1927) –

Meter is the length between two marks on a metal bar made of 90% platinum and 10% iridium alloy. This bar is maintained at constant temperature of 0^oC and is placed on two rollers. It is kept near Paris in France.

Definition of the meter (1988) –

Length of the path travelled by light in a vacuum in 1/299,792,458​ of a second.

To know more about the history of the meter, visit: History_of_the_metre

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MULTIPLES AND SUB-MULTIPLES OF METER

The unit meter is too small for measuring some lengths and too large for others. So, it was decided to increase it in multiple of 10 for large measures and decrease it by sub-multiples of 10 for small measures. These multiples and sub-multiples of the meter are given special names as given below:

Multiples of Meter

Decameter (dam), 1 dam = 10 meters = 10 m

Hectometer (hm), 1 hm = 100 meters = 100 m

Kilometer (km), 1 km = 1000 meters = 1000 m

Astronomical Unit (AU), 1 AU = 149,600,000,000 meters = 1496 x 10⁸ m

Light year (ly), 1 ly = 9,561,000,000,000,000 meters = 9461 x 10¹² m

We use the astronomical unit and the light-year to measure a distance between objects with an extremely large distance between them. Such as distances between planets and galaxies in the Universe.

Sub-multiples of Meter

Decimeter (dm), 1 dm = 0.1 meters = 1.0 x 10^-1  m or 1 m = 10 dm

Centimeter (cm), 1 cm = 0.01 meters = 1.0 x 10^-2  m or 1 m = 100 cm

Millimeter (mm), 1 mm = 0.001 meters = 1.0 x 10^-3  m or 1 m = 1,000 mm

Micrometer (μm), 1 μm = 0.000001 meters = 1.0 x 10^-6  m or 1 m = 1,000,000 μm

Nanometer (nm), 1 nm = 0.000000001 meters = 1.0 x 10^-9  m or 1 m = 1,000,000,000 nm

Angstrom (Å), 1 Å = 0.0000000001 meters = 1.0 x 10^-10  m or 1 m = 10,000,000,000 Å

We use units like the Nanometer and the Angstrom for the measurement of extremely small sizes, such as the diameter of atoms or molecules.

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OTHER UNITS FOR MEASUREMENT OF LENGTH

Apart from the units mentioned above, some people use foot, inch, yard and mile as units for measurement of length.

Inch (in), 1 in = 2.54 cm

Foot (ft), 1 ft = 12 in or 30.48 cm

Yard (yd), 1 yd = 3 ft or 36 in or 91.44 cm

Mile (mi), 1 mi = 1760 yd or 5280 ft or 63,360 in

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INSTRUMENTS USED FOR MEASUREMENT OF LENGTH

In ancient times, people used to measure the length with the help of body parts, such as outstretched palm, foot, arm-length (cubit). But you can see that such instruments cannot serve as the standard for measuring length. The simple reason is that they are going to be different for different people. So, to avoid confusion scientists developed standard instruments to measure length. The standard instruments are those which are acceptable to the majority of the people as a basic instrument for carrying out the measurement. Some of the standard instruments used to measure length are a ruler, meter scale, measuring tape, vernier caliper, and screw gauge.

To measure very long lengths like the length of a road we use measuring tape or an odometer. An odometer is an instrument for measuring the length or the distance traveled by a wheeled vehicle like car, trucks, etc.

For measuring very small lengths like the thickness of nail or paper, we use vernier caliper and screw gauge. For other common measurements of day to day household objects, we use ruler and meter scale.

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