Revision Term 1 Tg Physical Science Class 9

# Class 9 Physical Science: A Comprehensive Guide to Term 1

Welcome to your comprehensive guide for the first term of Class 9 Physical Science. This course is meticulously designed to help you master the fundamental concepts of matter, motion, forces, and energy, providing a robust foundation for your future studies in both physics and chemistry. By engaging with this material, you will develop the critical thinking and problem-solving skills necessary for success in the world of science. [1]

## Chapter 1: Introduction to Physical Science

Physical science is the systematic study of the inorganic world, focusing on the nature of matter and energy and how they interact. It is a vast field that is traditionally divided into two main branches: **physics** and **chemistry**.

**Physics** is the science of matter, motion, energy, and force. It seeks to understand the fundamental principles that govern the universe. Physicists study everything from the smallest subatomic particles to the largest galaxies, exploring concepts like gravity, electricity, magnetism, and the nature of light and sound. The principles of physics are foundational to many other scientific fields and have led to technological advancements that shape our daily lives, including electricity generation, telecommunications, and medical imaging.

**Chemistry**, on the other hand, is the science of the composition, structure, properties, and reactions of matter. Chemists study how atoms bond together to form molecules, how molecules interact with each other, and how substances can be transformed into new substances. Chemistry is often called the “central science” because it connects physics with other natural sciences such as biology and geology. It is essential for developing new materials, medicines, and energy sources. [2]

### The Scientific Method: A Framework for Inquiry

At the heart of all scientific disciplines is the **scientific method**, a structured and iterative process for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge. This method provides a logical framework for inquiry and is essential for understanding how scientific knowledge is generated, tested, and refined over time. The key steps include:

1. **Observation:** The process begins with careful observation of a phenomenon in the natural world. This can be something as simple as noticing that an apple falls from a tree or as complex as observing the light from a distant star.
2. **Question:** The observation leads to a question, such as “Why do objects fall to the ground?” or “What are stars made of?”
3. **Hypothesis:** A testable explanation, or hypothesis, is formulated to answer the question. A good hypothesis is a specific, falsifiable statement, such as “Objects fall to the ground because they are attracted to the Earth by a force called gravity.”
4. **Experimentation:** A controlled experiment is designed and conducted to test the hypothesis. In a controlled experiment, one variable (the independent variable) is changed to observe its effect on another variable (the dependent variable), while all other conditions (controlled variables) are kept constant.
5. **Analysis:** The data collected from the experiment is analyzed to identify patterns, trends, and relationships. This often involves mathematical calculations and graphical representation.
6. **Conclusion:** A conclusion is drawn based on the analysis, stating whether the results support or refute the hypothesis. If the hypothesis is refuted, it must be modified or discarded, and the process begins again. If it is supported, it can be further tested through repeated experimentation.

This process is not always linear; the results of an experiment often lead to new questions and further investigation. A hypothesis that has been repeatedly tested and confirmed by many different scientists can become a **theory**, which is a well-substantiated explanation of some aspect of the natural world. [2]

## Chapter 2: The Nature of Matter

Everything you can see, touch, and feel is made of matter. In this chapter, you will delve into the fundamental nature of matter, exploring its different states and the properties that distinguish one substance from another. [1]

### The Particle Nature of Matter and Kinetic Theory

All matter is composed of incredibly tiny particles called **atoms** and **molecules**. The **kinetic theory of matter** is a model that explains the physical properties of matter in terms of the motion of its constituent particles. The main postulates of this theory are:

* All matter is made up of a large number of tiny particles.
* These particles are in constant, random motion.
* There are forces of attraction between the particles. The strength of these forces determines the state of matter.
* The average kinetic energy of the particles is directly proportional to the absolute temperature of the substance.

Evidence for this constant motion can be seen in the phenomenon of **diffusion**, the net movement of particles from a region of higher concentration to a region of lower concentration, and **Brownian motion**, the random movement of particles suspended in a fluid (a liquid or a gas) resulting from their collision with the fast-moving atoms or molecules in the fluid. [3]

### States of Matter: Solids, Liquids, and Gases

Matter commonly exists in three states on Earth: solid, liquid, and gas. A fourth state, plasma, is the most abundant in the universe, found in stars and lightning.

| State | Particle Arrangement | Particle Motion | Inter-particle Forces | Shape & Volume | Compressibility |
| :— | :— | :— | :— | :— | :— |
| **Solid** | Tightly packed in a fixed, regular pattern (crystal lattice) | Vibrate about fixed positions | Very strong | Definite shape and volume | Incompressible |
| **Liquid** | Close together but randomly arranged | Move past one another | Strong | Indefinite shape, definite volume | Nearly incompressible |
| **Gas** | Far apart and randomly arranged | Move rapidly and randomly | Very weak | Indefinite shape and volume | Highly compressible |

### Changes of State and Latent Heat

Matter can transition between states through processes driven by the addition or removal of thermal energy. These transitions are physical changes.

* **Melting:** Solid to liquid (e.g., ice to water)
* **Freezing:** Liquid to solid (e.g., water to ice)
* **Evaporation/Boiling:** Liquid to gas (e.g., water to steam)
* **Condensation:** Gas to liquid (e.g., steam to water)
* **Sublimation:** Solid to gas (e.g., dry ice to carbon dioxide gas)
* **Deposition:** Gas to solid (e.g., water vapor to frost)

During a change of state, the temperature of the substance remains constant even though heat is being added or removed. This energy is called **latent heat**. The **latent heat of fusion** is the energy required to change a solid to a liquid at its melting point, and the **latent heat of vaporization** is the energy required to change a liquid to a gas at its boiling point. This energy is used to overcome the forces of attraction between particles, not to increase their kinetic energy. [1]

### Physical vs. Chemical Changes

It is crucial to distinguish between physical and chemical changes.

* A **physical change** alters the form or appearance of a substance but does not change its chemical identity. No new substances are formed. Examples include changes of state, dissolving, cutting, and crushing.
* A **chemical change**, or chemical reaction, results in the formation of one or more new substances with different properties. The original substances are used up. Indicators of a chemical change include a significant change in color, the production of a gas (effervescence), the formation of a solid precipitate, or the release or absorption of energy (heat, light, or sound). [4]

## Chapter 3: Motion and Kinematics

Kinematics is the branch of physics that describes motion without considering its causes. Understanding the language of motion—distance, displacement, speed, velocity, and acceleration—is key to describing the world around us. [1]

### Scalar and Vector Quantities

In physics, quantities are classified as either scalars or vectors.

* **Scalars** are quantities that are fully described by a magnitude (or numerical value) alone. Examples: distance (5 m), speed (20 m/s), mass (10 kg), time (15 s), temperature (300 K).
* **Vectors** are quantities that are fully described by both a magnitude and a direction. Examples: displacement (5 m, East), velocity (20 m/s, North), force (10 N, downwards), acceleration (9.8 m/s², downwards).

### Describing Motion: Distance, Displacement, Speed, and Velocity

* **Distance** is a scalar quantity that refers to “how much ground an object has covered” during its motion. It is the total path length.
* **Displacement** is a vector quantity that refers to “how far out of place an object is”; it is the object’s overall change in position, measured in a straight line from the start point to the end point.
* **Speed** is a scalar quantity that refers to “how fast an object is moving.” Average speed is calculated as total distance divided by total time.
* **Velocity** is a vector quantity that refers to “the rate at which an object changes its position.” Average velocity is calculated as total displacement divided by total time.

### Acceleration

**Acceleration** is a vector quantity defined as the rate of change of velocity. An object is accelerating if its velocity is changing. This can mean it is:

1. Speeding up (positive acceleration)
2. Slowing down (negative acceleration or deceleration)
3. Changing direction (as in circular motion)

### Graphical Analysis of Motion

Graphs are powerful tools for visualizing and analyzing motion.

* **Distance-Time Graphs:** The slope (gradient) of a distance-time graph represents the object’s speed. A horizontal line means the object is stationary. A straight, non-horizontal line means constant speed. A curved line means changing speed (acceleration).
* **Velocity-Time Graphs:** The slope of a velocity-time graph represents the object’s acceleration. The area under a velocity-time graph represents the object’s displacement. A horizontal line means constant velocity (zero acceleration). A straight, non-horizontal line means constant acceleration.

### Equations of Motion (for Uniform Acceleration)

For an object moving with constant acceleration, its motion can be described by three key kinematic equations:

1. `v = u + at` (relates final velocity, initial velocity, acceleration, and time)
2. `s = ut + (1/2)at²` (relates displacement, initial velocity, acceleration, and time)
3. `v² = u² + 2as` (relates final velocity, initial velocity, acceleration, and displacement)

Where: `s` = displacement, `u` = initial velocity, `v` = final velocity, `a` = acceleration, and `t` = time. These equations are essential for solving a wide range of problems in kinematics. [1]

## Chapter 4: Force and the Laws of Motion

Dynamics is the study of the causes of motion, namely forces. A **force** is a push or a pull that can cause an object with mass to change its velocity (i.e., to accelerate). Forces can also change an object’s shape. The principles governing the relationship between force, mass, and motion were famously formulated by Sir Isaac Newton. [5]

### Newton’s First Law: The Law of Inertia

Newton’s First Law states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external, unbalanced force. This property of an object to resist changes in its state of motion is called **inertia**. The more mass an object has, the greater its inertia. This is why it is much harder to push a car than a bicycle. [5]

### Newton’s Second Law: The Law of Acceleration

Newton’s Second Law provides a quantitative relationship between force, mass, and acceleration. It states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. The direction of the acceleration is in the direction of the net force. This is famously expressed by the equation:

**F_net = ma**

Where `F_net` is the net or resultant force in newtons (N), `m` is the mass in kilograms (kg), and `a` is the acceleration in meters per second squared (m/s²). This is one of the most important equations in all of physics. [5]

### Newton’s Third Law: The Law of Action-Reaction

Newton’s Third Law states that for every action, there is an equal and opposite reaction. This means that forces always occur in pairs. If object A exerts a force on object B, then object B simultaneously exerts a force of equal magnitude and opposite direction on object A. It is important to remember that these two forces act on *different* objects and therefore do not cancel each other out. For example, when you walk, your foot pushes backward on the ground (action), and the ground pushes forward on your foot (reaction), propelling you forward. [5]

## Chapter 5: Gravitation

Gravitation is the fundamental force of attraction that exists between any two objects with mass. It is the weakest of the four fundamental forces but acts over infinite distances. It is the force that holds the planets in orbit around the sun, keeps the moon in orbit around Earth, and causes objects to fall to the ground. [5]

### Newton’s Law of Universal Gravitation

Newton’s law of universal gravitation states that every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. The equation is:

**F = G (m₁m₂ / r²)**

Where `F` is the gravitational force, `m₁` and `m₂` are the masses of the two objects, `r` is the distance between their centers, and `G` is the universal gravitational constant (approximately 6.674 × 10⁻¹¹ N⋅m²/kg²). [5]

### Mass vs. Weight

It is crucial to distinguish between mass and weight.

* **Mass** is an intrinsic property of an object, representing the amount of matter it contains. It is a measure of an object’s inertia. Mass is a scalar quantity measured in kilograms (kg) and is the same everywhere in the universe.
* **Weight** is the force of gravity acting on an object’s mass. It is a vector quantity measured in newtons (N). An object’s weight can change depending on its location and the strength of the local gravitational field (`Weight = mass × gravitational field strength`, or `W = mg`). For example, an astronaut has the same mass on the Moon as on Earth, but their weight is only about one-sixth as much because the Moon’s gravitational field is weaker. [5]

## Chapter 6: Work, Energy, and Power

Work, energy, and power are interconnected concepts that are central to physics. They describe how forces can change the state of a system and the rate at which these changes occur. [6]

### Scientific Definition of Work

In physics, **work** is done on an object when an applied force causes the object to be displaced in the direction of the force. For work to be done, two conditions must be met: a force must be applied, and the object must move. The formula for work is:

**Work = Force × Distance** (W = Fd)

Work is a scalar quantity measured in joules (J). One joule is the work done when a force of one newton moves an object one meter. [6]

### Energy: The Ability to Do Work

**Energy** is defined as the capacity to do work. Like work, it is a scalar quantity measured in joules (J). Energy exists in many forms, and the two main types in mechanics are:

1. **Kinetic Energy (KE):** The energy an object possesses due to its motion. It depends on the object’s mass and the square of its velocity: `KE = (1/2)mv²`
2. **Potential Energy (PE):** Stored energy an object has due to its position or state. A common form is gravitational potential energy, which depends on the object’s mass, the gravitational field strength, and its height: `PE = mgh`

Other forms of energy include chemical energy, thermal energy, electrical energy, and nuclear energy.

The **Law of Conservation of Energy** is a fundamental principle stating that energy cannot be created or destroyed in an isolated system, only converted from one form to another. For example, as a ball falls, its potential energy is converted into kinetic energy. [6]

### Power: The Rate of Doing Work

**Power** is the rate at which work is done or the rate at which energy is transferred or transformed. It is a measure of how quickly work can be done. The formula for power is:

**Power = Work / Time** or **Power = Energy / Time** (P = W/t)

Power is a scalar quantity measured in watts (W), where 1 watt is equal to 1 joule per second. A more powerful engine can do the same amount of work in less time. [6]

## Conclusion

This guide has provided a thorough revision of the key concepts covered in the first term of Class 9 Physical Science. By understanding the nature of matter, the principles of motion, the fundamental laws of forces, and the concepts of work and energy, you have built a strong foundation for your ongoing journey in science. Continue to be curious, ask questions, and apply these principles to the world around you. Good luck with your studies!

## References

[1] Khan Academy. (n.d.). *Revision Term 1 – TG Physical Science Class 9*. [https://www.khanacademy.org/science/revision-term-1-tg-physical-science-class-9](https://www.khanacademy.org/science/revision-term-1-tg-physical-science-class-9)

[2] Teachers Pay Teachers. (n.d.). *Physical Science Curriculum – Full Year Integrated Physics and Chemistry Course*. [https://www.teacherspayteachers.com/Product/Physical-Science-Curriculum-Full-Year-Integrated-Physics-and-Chemistry-Course-3299240](https://www.teacherspayteachers.com/Product/Physical-Science-Curriculum-Full-Year-Integrated-Physics-and-Chemistry-Course-3299240)

[3] YouTube. (2025, December 10). *Explaining States of Matter & Brownian Motion | Grade 9 Physics*. [https://www.youtube.com/watch?v=IAZCt0L6D44](https://www.youtube.com/watch?v=IAZCt0L6D44)

[4] YouTube. (2021, September 13). *Physical Science Grade 9, Lessons 1 – 4*. [https://www.youtube.com/watch?v=NXaR7eN3-2E](https://www.youtube.com/watch?v=NXaR7eN3-2E)

[5] Scribd. (n.d.). *9th Physics Syllabus Term 1*. [https://www.scribd.com/document/838038050/9th-Physics-Syllabus-Term-1](https://www.scribd.com/document/838038050/9th-Physics-Syllabus-Term-1)

[6] Magnet Brains. (n.d.). *Class 9th Physics Science Book (NCERT) – Full Video Course*. [https://www.magnetbrains.com/course/class-9th-physics-science-book-ncert-full-video-course/](https://www.magnetbrains.com/course/class-9th-physics-science-book-ncert-full-video-course/)