Subject: Science
The process of comparing an unknown physical quantity with known standard quantity is called measurement. This note contains information about measurement and different quantities related to measurement.
The accurate quantity of a substance can only be known by measurement. Measurement can be expressed in figures and in standard measurement. We use different instruments like measuring tape or scale for the measurement of length, beam balance for measuring masses and clock for the measurement of time.
The process of comparing an unknown physical quantity with a known standard quantity of the same kind is called measurement. Measurement is essential to know the exact physical quantity of the substances in our daily life. Those substances which are available in our surrounding can be measured are known as physical quantities. Some of the examples of physical quantities are the area, mass, time, length, temperature, etc. Those things which cannot be measured are called non- physical quantity. Some of the examples of non- physical quantity are love, kindness, anger, interest, feelings etc. There are two types of physical quantities. They are discussed below,
Without measurement, we cannot estimate the total amount of physical quantity.
Fundamental unit
Those units whose value do not depend on any other units are fundamental units. For example, Length of an object i.e meter, the mass of an object i.e kilogram, time i.e second.
Here are the seven fundamental units used to measure the fundamental quantities:
Fundamental quantity | Unit | Symbol |
Length | Meter | m |
Mass | Kilogram | kg |
Time | Second | s |
Temperature | Kelvin | K |
Electric current | Ampere | A |
Luminous intensity | Candela | cd |
Amount of substance | Mole | mol |
Derived Unit
Those units whose value depend on other units are derived units. For example, To measure the velocity of a car we must know the distance traveled by car and time taken by the car to travel the distance.
S.N | Derived Quantities | Derived Units | Symbol |
1. | Area | Square meter | m^{2} |
2. | Volume | Cubic meter | m^{3} |
3. | Density | Kilogram per cubic meter | kg/ m^{3} |
4. | Speed/Velocity | Meter per second | m/s |
5. | Acceleration | Meter per second per second | m/s^{2} |
6. | Force | Newton | N |
7. | (work/energy) | Joule | J |
8. | Power | Watt | W |
9. | Pressure | Pascal | Pa |
There are different units of fundamental quantities that combine together to form a system of units. There are four systems of unit of measurement:
A. FPS system:
The full form of this system is Foot- Pound and second system. In this system, the fundamental units of length, mass and time are foot, pound and second.
B. CGS system
The full form of this system is Centimeter- Gram- Second system. In this system, the fundamental units of length, mass and time are centimetres, gram, and second.
C. MKS system
The full form of this system is Meter- Kilogram- Second system. In this system, the fundamental units of length, mass and time are meters, kilogram and second.
D. SI system
The full form of this system is System de international Unit. This system is modified form of MKS system. This system includes seven fundamental units such as the unit of electricity- Ampere (A), unit of temperature- kelvin (K), unit of light- Intensity (I) and the unit of amount of matter- mole (mol) along with three fundamental units of MKS system i.e. meter, kilogram and second.
What is a physical quantity?
The substance which is available in our surroundings or can be measured is called a physical quantity. For example, length, mass, time, volume, etc.
What is the unit?
The certain standard quantity which is used for the measurement of an unknown quantity is called unit of that quantity.
The fundamental unit is the unit which is independent of other units. In other words, the unit of length, mass and time are called fundamental units.
What is a derived unit?
The physical quantity which is derived from other quantities and dependent on other physical quantities is called a derived unit.
A system of physical units based on the meter, kilogram, second and mole together with a set of prefixes to indicate multiplication or division by a power of ten is called SI unit.
Why is measurement necessary in our daily life?
Measurement is necessary for our daily life because the accurate quantity of a substance can be known through measurement.
Differentiate between the fundamental unit and derived unit.
Fundamental unit | Derived unit | |
The unit of length, mass and time are the fundamental units. | The unit made from fundamental units are derived unit. | |
These quantities are directly measurable in a physical system. | These quantities can be derived using fundamental units. | |
Fundamental units are defined independently. | These units are not defined independently. |
What are units of SI system of measurement?
Meter, Kilogram , Second , Kelvin , Ampere , Mole and Candela are units of SI system of measurement.
Express in metres.
a) 300 cm
We have,
\begin{align*} 300 \: cm &= \frac {300}{100} \: m = 3\: m \:\:\: \left [ \because 1 \: m = 100 \: cm \right ] \\ \therefore 300 \: cm &= 3\: m \\ \end{align*}
b) 2.56 km
We have,
\begin{align*} 2.56 \: Km &= 2.56 \times 1000 \: m = 2560\: m \:\:\: \left [ \because 1 \: k m = 1000 \: m \right ] \\ \therefore 2.56\: Km &= 2560\: m \\ \end{align*}
c) 3.78 mm
We have,
\begin{align*} 3.78 \: mm = \frac {3.78}{10} \:c m = 0.387\: cm \:\:\: \left [ \because 1\: cm = 10 \: mm \right ] \\ \text {changing cm into mm} \\ 0.378 \: cm = \frac {0.378}{100} m = 0.378 \times 10^{-2} \:\:\: \left [ \because 1 \: m = 100 \: cm \right ] \\ \therefore 3.78 \: mm = 0.378 \times 10^{-2}\: m \\ \end{align*}
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