Basics of Measurement for Kids | SI Units

Measurement is not only for kids – it is the necessity of a life of every one of us. 

Daily, we come across situations when we measure length, mass, time and temperature. For example,

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  Measuring Weight of Vegetable

  When you try to find out a distance between your house and your friend’s house, you measure length.

• If you want to know the quantity of vegetables or grocery items you need to buy, you measure mass or weight.
• When you try to find out how long will it take you to complete your homework, you measure time.
• When you want to know how cold or hot your milk is, you measure its temperature.

TOPICS COVERED:

• Importance of measurement for kids
• Definition for measurement for kids
• Important terms
  • Physical Quantities
  • Unit of Measurement
  • Standard units
  • Multiples and Sub-multiples

IMPORTANCE OF MEASUREMENT

Measurement is an essential need to keep accuracy in our various day-to-day activities. Without actual measurement, we cannot make a correct judgment about the length, mass, time, temperature, etc of a given object. For example, when you feel sick, your mother measures your body temperature with the help of a thermometer. The thermometer shows 100^oF temperature. So, do you have a fever? Yes, since our normal body temperature is 98.6^oF, thus any value above it confirms that you are suffering from fever. It means that on measuring your body temperature, she would know exactly you have a fever or not. So, in this case, the accurate measurement of temperature is very important.

Very often people make guesses. We can guess how far New York is from Chicago or how warm this room is. Estimates are guess made based on our knowledge and common sense. Estimates are often very useful, but they are not exact and can sometimes be very wrong. However, most of the measurements we make in physics, need to be fairly accurate. For example, if we have to lay a railway line from New York to Chicago than each kilometer of distance matters. Thus, estimation, in this case, can lead to a short or long railway line. So, to avoid such a mistake, we need to carry out an accurate measurement of the distance between two railway stations in Chicago and New York.

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DEFINITION OF MEASUREMENT FOR KIDS

Measurement is a comparison of an unknown quantity with a known fixed quantity.

IMPORTANT TERMS RELATED TO MEASUREMENT

Before we can proceed further with the measurement of length, mass, time and temperature, you need to understand the following terms:

A. PHYSICAL QUANTITY

A quantity that can be measured is a physical quantity. Length, time, mass and volume are some examples of a physical quantity.  For example, you cannot measure the level of love, anger, sincerity, honesty, etc. of your friend, however, you can measure his height, weight and body temperature. Thus in the present example, the former are not physical quantities whereas later one is. Physical quantities are of two types:

1. Fundamental Physical Quantities: These are quantities that are completely independent of each other and do not depend upon any other quantities.  For example, mass, length, time and temperature.
2. Derived Physical Quantities: These quantities are obtained by combining two or more fundamental quantities. For example, area (it depends on length and breadth), speed (depends on distance and time), etc.

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B. UNITS OF MEASUREMENT

During measurement, we compare the unknown quantity of things or substances with a known fixed quantity. This fixed quantity with which we compare unknown quantity is called a unit of measurement. For example, when someone request for 5 glass of water, then here ‘a glass of water‘ is unit and person is requesting for 5 unit of the same. Hence to express the result of a measurement of a physical quantity, we must know:

1. the unit in which the quantity is to be measured, and
2. the numerical value which expresses how many times the above-mentioned unit is there in the given quantity.

Let us take one more example,

If the length of a piece of cloth is 10 meters, it means that we measure the length in the unit ‘meter’ and this unit is present 10 times in the length of that piece of cloth. Thus, a measurement consists of two parts – the magnitude (or number) and a unit.

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C. STANDARD UNITS OF MEASUREMENT

In the past, people used different units used for measurement in different countries. For example, people in ancient times used their footsteps, arm-length, hand-span, ropes, sticks, etc to measure length. One arm-length (cubit) was the length from the elbow to the tip of the middle finger of a person’s hand. Similarly, a hand-span was the length from the tip of the thumb to the tip of the little finger of the completely stretched hand.

In the past, when an object was measured with a cubit or hand-span, its length varied from person to person. The simple reason for the variation was the difference in the size of the cubit or hand-span of each person. Thus, this system of measurement was inconvenient as well as inaccurate. So, to maintain uniformity in measurement, scientists from all over the world accepted some of the units as standard units. This set of units is generally referred to as Standard International or SI system of units.

Definition of Standard International or SI Unit –

Standard International or SI unit is the unit which is acceptable to majority of the people as a basic unit of measurment.

Standard International or SI units for measurement of length, mass, time and temperature are given below:

Quantity	Unit	Symbol
Length	Meter	m
Mass	Kilogram	Kg
Time	Second	s
Temperature	Kelvin	K

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D. MULTIPLE AND SUB-MULTIPLE UNITS

Sometimes, standard units or SI Units are not convenient for expressing the measurement of very large or very small quantities. In such cases, we use multiples or sub-multiples of these standard units.

Let us understand by an example,

To measure the distance between two far-off cities, say Chicago and New York, measuring in meters is not only difficult but very inconvenient too. Hence, we use some bigger unit, say, kilometer, which is a multiple of a meter.

1 kilometer = 1000 meters

In short, 1 km = 1000 m

Now, thus instead of saying the distance between Chicago and New York as 1,250,000 m, we say it is 1250 km, which is far more convenient.

Similarly, if we are measuring the length of an eraser or a pen, or say, our nails we again cannot depend on the unit meter but we need some smaller or sub-multiple units like centimeter (cm) or millimeter (mm).

1 meter = 100 centimeters or 1000 millimeters

In short, 1 m = 100 cm or 1000 mm

1 cm = 10 mm

So, it convenient to express the diameter of a coin as 2 cm instead of 0.02 m or size of the tip of a pen as 1 mm instead of 0.001 m.

Now kids, as you have learned basics of measurement, thus you can proceed to an advanced level by going through my specific posts related to the measurement of length, mass, time and temperature.

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