Physical quantities and measurement

Physical quantities and measurement

What is a physical quantity?

A quantity that can be measured is called a physical quantity. They are of 2 types.

Multiple Choice

What are physical quantities?

• Quantities that can be measured

• Quantities that cannot be measured

• Quantities that have a magnitude and unit

• Quantities that are 'physical'

Types of physical quantities-

• Fundamental physical quantity

• Derived physical quantity

Multiple Choice

How many types of physical quantities are there?

• 2

• 3

• 1

• 4

Fundamental physical quantities-

Basic quantities that do not depend on any other physical quantity is called a fundamental physical quantity. There are 7 of them.

The 7 fundamental physical quantities-

• Mass (Kilogram-Kg)

• Length (meter-m)

• Time (second-s)

• Temperature (Kelvin-K)

• Luminous intensity (candela-cd)

• Amount of substance (mole-mol)

• Electric current (ampere-A)

Mass is not to be confused with weight-

Mass is the amount of matter an object has, it is a fundamental physical quantity, it is measured in Kg (Kilogram), whereas weight is a derived physical quantity, it is the force of gravity acting upon an object. it is derived from Mass and Gravity (M x G), you will probably study that in 7th or 8th. Weight is measured in newton.

Multiple Choice

How many fundamental physical quantities are there?

• 7

• 5

• 4

• 6

Derived physical quantities

Physical quantities that are derived from one or more fundamental physical quantities are called derived physical quantities. Eg- Speed, it i derived from length and time.

Multiple Choice

Are derived physical quantities dependent on any other physical quantity?

• Yes

• No

Measurement

Measurement is the act of measuring something, or, if you want to sound smart while saying it, it is the determination of the exact value of an unknown physical quantity with a known fixed physical quantity of the same kind. Eg- You measure your height. You are comparing the length of the measuring tape or whatever you are using, with the height of your body. The length of the tape is known, and the length of your body is unknown, therefore we can say that- Measurement is the determination of the exact value of an unknown physical quantity with a known fixed physical quantity of the same kind.

Some extra things to note-

• The measurement of a physical quantity consists of 2 parts- the unit and the magnitude

• The magnitude is the number of units the measured quantity has. Eg- In 12cm, 12 is the magnitude.

• The unit is a fixed known physical quantity that is used for comparison with an unknown physical quantity in measurement. Eg- in 12cm, cm (centimeter) is the unit.

Multiple Select

Measurement has _ parts/part.

• 3

• 2

• 1

• 4

Ancient ways of measurement of length and time-

In the ancient times, people used their body parts to measure length. Cubit and Handspan were popular ways of measuring length. The Greeks also invented the Sundial. Which worked on the principle that the shadow of a rod placed in it changes it's shape, size and position with the changing position of the Sun.

A sundial

The F.P.S System

In the medieval times, the British invented a system for measurement that used 'foot' as the unit for length, pound for mass and second for time. Each foot consisted of 12 inches, each inch being the length of 3 barleycorns. (An Inch nowadays is 2.54 cm)

The Metric system-

In 1719, the French created a measurement system, the Metric system, it was a simple and scientific system. It used centimeter as the unit for length, gram for mass and liter for volume. As the years passed, this system game rise to 2 new systems- The MKS and CGS systems.

The CGS and MKS systems

The CGS system and the MKS system were different variants of the Metric system. The CGS system had centimeter as a unit for length, gram for mass and second for time. The MKS system had meter as a unit for length, Kilogram for mass and second for time. At a time, the MKS sytem was more popular than the CGS. (Note: All three system, FPS, CGS and MKS have the same unit for time, second)

Multiple Choice

What were the four systems?

• FPS, CMS, Metric and MGS

• FPK, CGS, Metric and MGN

• FKS, CSK, Metric and MGN

• FPS, CGS, Metric and MKS

The SI system-

The existence of two systems led to confusion among the users, so during the twentieth century (1960) the General Conference of Weights and Measures met in Paris, and adopted the International system for Units.

Multiple Choice

When did the General Conference of Weights and Measures meet?

• 1970

• 1960

• 1968

• 1962

That's all for today!

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