Table of Contents

The Système Internationale’ Unites (French for International System of Units), shortened as SI, is the international measurement system now in use. The SI was established and recommended by the General Meeting on Weights and Measures in 1971 for global use in scientific, technical, industrial, and commercial activities, with a consistent scheme of symbols, units, and abbreviations. Because SI units are based on the decimal number system, conversions within the framework are easy and straightforward. The FPS system is typically used for extremely large measurements, such as room size. The CGS system is being used for very small length and mass measurements, whereas the MKS system is used for big masses, and the SI units system is widely used and appropriate for practically all measurements.

The number of units is equal to the number of independent quantities. We investigate three quantities that are unrelated to one another: length, mass, and time. As a result, they have three different measurement units. As a result, unit systems must be defined.

A system of units is a group of units in which some units are designated as fundamental and all others are descended from them. This system is sometimes known as an absolute unit system. Mass, length, and time are regarded as fundamental quantities in most systems, and their units are called primary units. Below are some of the most often used unit systems.

**c.g.s. system of measurement**:

The centimetre is the measurement unit for length (cm). The gram is the unit of mass (g). The second is the metric unit of time (s)

**m.k.s. system of measurement**:

The metre is the measurement unit for length (m). The kilogram is the unit of mass (kg). The second is the metric unit of time (s)

**f.p.s. system of measurement**:

A foot is a measurement of length (ft). A pound is a unit of mass (Lb). The second is the metric unit of time (s). This system does not exist operational.

**A Brief Outline**

The traditional metric system has been improved and extended by this set of units. In all disciplines of science, engineering, industry, and technology, this system of units has now replaced all other systems of units.

- All units and symbols, such as centimetres (cm), metre (m), and kilogram per metre cube, should be written in small case letters (kg m-3).
- The units named after scientists do not have a capital initial letter, but their symbol is in capital letters. As a result, instead of ‘Newton,’ the unit of force is denoted as ‘newton’ or ‘N.’
- In a composite unit, the denominators should be written with negative powers. As a result, when writing a derived unit, an index notation should be utilized. Instead of m/s, the unit of velocity should be represented as ms-1. Density is measured in kilograms per metre cube (kg m-3, not kg/m3).
- A compound unit is formed by inserting a dot between symbols of two or more physical quantities, or by leaving a space between symbols of two or more physical quantities. The newton metre (Nm or N.m) is an example of a torque unit. The newton second (N s or N.s) is the unit of impulse.
- Between the number and its unit, there should be some gap.

**Steps to Identify a Derived Unit in General:**

**Step 1**: Create the equation for the quantity whose unit is now to be derived.

**Step 2**: Substitute fundamental or standard units for all quantities in a single system of units.

**Step 3**: Reduce and find the quantity’s derived unit.

For e.g.: **To determine the velocity unit.**

The term “velocity” refers to a resultant quantity. As an effect, its unit is derived.

The velocity is calculated using the formula velocity = displacement/time.

m/s = S.I. unit of velocity = S.I. unit of displacement/ S.I. unit of time = S.I. unit of velocity

As a result, the S.I. The unit of velocity is m/s.

A unit is a specific physical amount that is defined and approved by convention and used to compare and represent the value of other specific quantities of the same kind. A physical quantity is one that can be employed in scientific and engineering mathematical calculations.

Physical quantity’s value is the numerical expression of that amount as the product of a number and a unit, with the number being its numerical value. The numerical value of a physical quantity is thus determined by the unit in which it is stated. It is normal to document both the quantity (how much) and the unit when taking measurements (of what). The unit of measurement is crucial in science and technology.

The height h of a building, for instance, is h = 120 m. The physical quantity h has a value of 120 m when stated in the unit “meter,” unit sign m, and a numerical value of 120 when expressed in meters. As scientists improvised to fulfill the practical needs of their professions, rapid breakthroughs in research and technology in the 19th and 20th centuries spurred the development of numerous overlapping systems of units of measurement. The meter-kilogram-second (MKS) system was an early international system developed to remedy this problem.

In 1948, the CGPM introduced three new units: a newton, which is defined as the force that causes a mass of one kilogram to accelerate by one meter per second per second; a joule, which is characterized as the work done whenever the position of application of a newton is shifted one metre in the direction of force; and a watt, which is defined as the power that produces one joule of energy in one second. Each of the three units is named after a well-known scientist.

In terms of basic physical constants, the CGPM revised the kilogram, ampere, mole, and kelvin. Planck’s constant, which is specified as 6.62607015* 10 34 joule second, was chosen as the constant for the kilogram. One joule is one kilogram multiplied by the square of the metre per second squared. The kilogram would subsequently be determined by precise measurements of Planck’s constant, as the second and metre had previously been defined.

**Significance of units of measurement for NEET exam**

On Infinity learn’s official website, students can obtain the **NEET** key questions on Units and Measurements in PDF format. It is absolutely free and has been thoroughly revised by a physics instructor with extensive experience. This content assists students in determining which concepts are the most significant, as well as providing relevant explanations and examples for these topics.

**The following are some examples of sample questions:**

**1. A driving force F = at + bt2, where t is time, yields F. What are a and b’s measurements?**

- MLT-3 and ML2T4
- MLT-4 and MLT1
- MLT-3 and MLT-4
- MLT-1 and MLT0

The solution is (c).

**2. A particle moves in the (x, y) plane in a straight path starting at the origin (0, 0). Its coordinates represent the angle of the particle’s path with the x-axis at a later time.**

- 600
- 450
- 0
- 300

The solution is (a).

**Frequently asked questions (FAQs)**

**Q. Why is the decimal-based system called the metric system?**

**Ans:** Because it is based on multiples of ten, the metric system is known as the decimal-based system. Any metric measurement, such as kilogram, can be converted to another unit, such as gram, by simply shifting the decimal place. Because it allows for the depiction of units using decimal points, the metric system is sometimes known as the decimal-based system.

**Q. Is it true that the Infinity Learn notes on “Units of measurement” will help me prepare for my exams?**

**Ans: **Units of measurement are an essential chapter in math that receives a lot of attention on the exam. As a result, it is critical to learn the various topics linked with this chapter by using credible sources or reference notes. This chapter’s infinity learns notes provide the correct data in a concise structure and format to aid students in grasping the topics.

**Q. What is the definition of a unit?**

**Ans: **The unit is defined as the measurement’s standard of reference.