A lot of learners need help with the subject. It’s not particularly difficult, but it’s a highly technical subject. Many students are worried about their preparation and consider it to be a challenging subject. **Al Hamd Science Academy** has made this complex subject easy. We offer you a simple method for preparing. The notes for Physics Class 9 are the most effective for preparation. Notes for 9th-class physics are available now through our website.

**Physical Quantities & Measurement**

Introduction:

Measurement and physical quantities is 1st chapter of 9th class physics notes which play an essential role in comprehending world. Everything can be described using physical quantities, and measured with appropriate measurement units. This article will examine the idea of physical quantity, significance of measuring, and the different systems and instruments employed.

## 9th class physics notes | Chapter 1 –Physical Quantities & Measurement

### Physical Quantities:

Physical quantity refers to an attribute or characteristic of a thing that can be determined. It is a term used to describe an amount that can express numerically, typically with a measure. Physical numbers may be divided into two categories which are vector and scalar.

Scalar numbers are those with only magnitude and do not have a direction. Examples include temperature, mass, time, energy, and mass. The scalar quantity is represented by one numerical value and is added mathematically.

However, vectors have both direction and magnitude. Examples include displacement, velocity force as well as acceleration. The vector quantities are represented using both direction and magnitude and are added in a vector manner.

#### Measurement:

Measurement is the procedure of comparing an unidentified quantity against a standard or known amount of the same type. It is a vital tool for scientific research as well as manufacturing, engineering, and in everyday daily life. Precision and accurate measurements are essential for technological breakthroughs and scientific research advancements and to ensure the highest quality in all disciplines.

Measurement is a process that involves two main elements: a unit as well as an instrument for measuring. A unit is a basis for expressing the size of a physical amount. It lets us exchange and compare measurements across the world. Common measurements include kilograms, meters, seconds, and Kelvin, among others.

Instruments for measuring are instruments used to measure physical quantities. They are made to give exact and precise measurements. Commonly employed measuring instruments include balances, rulers, thermometers, voltmeters, and spectrometers. Technology advancements have resulted in the creation of more advanced instruments, such as laser interferometers, as well as the atomic force microscopes which provide greater sensitivity and accuracy.

**Systems of Measurement:**

Over the years, various methods of measuring were used by different societies and cultures. It is this system of measurement International System of Units (SI) was established as the standard measurement system.

This SI system is built on seven basic units that are meters (length) and kilogram (mass) as well as second (time) ampere (electric current), Kelvin (temperature) mole (amount of a substance) and the candela (luminous intensities). Mathematical relations derive the rest of the units from these basic units.

Apart from the SI system, There are different measuring systems like the imperial system and the United States customary system, which are still being used in some countries for routine uses. However the scientific community as well as many countries have adopted SI system to measure technical and scientific data to ensure uniformity as well as international cooperation.

##### Significant Figures:

When measuring, It is essential to think about the degree of accuracy and precision. Significant figures are a method to measure the precision of a quantity that is measured. They represent the number of digits that are reliable in a measurement, which includes all digits with certain values and one digit that is uncertain or not known.

Significant figures are derived according to the precision of the instrument being used. For instance, for a ruler that has markings of up to a millimeter, the measurements taken with this ruler may be measured with a accuracy as high as one-tenth of a millimeter.

Significant figures are crucial in calculations involving measurement quantities. The results of calculations should be rounded down to the right number of significant figures, based on the most precise measurement that was used for the analysis.

Conclusion:

Physical quantities and measurements are crucial to understanding the natural world and many technological and scientific applications. They serve as a basis for explaining and comparing phenomena, which allows us to make precise predictions and formulate accurate theories.

With the help of standard units and precise measuring tools which are faithful, we can get accurate and accurate measurements. The International System of Units (SI) is the world’s accepted measurement system that ensures consistency and facilitates international collaboration.

Knowing significant figures and managing measurements properly is vital to ensure the accuracy of scientific experiments and calculations.

In the end, studying physical quantities and measurements is a crucial element of scientific inquiry and technological advancement, allowing us to understand and explore the vastness that exist in the world.