Grade 9
  1. Mechanics  1.1. Motion  1.1.1. Types of motion  1.1.2. Distance and displacement  1.1.3. Speed and Velocity  1.1.4. Acceleration  1.1.5. Graphical representation of motion  1.1.6. Equations of motion  1.1.7. Uniform and non-uniform motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Relative speed  1.1.10. Circular motion  1.2. Laws of force and motion  1.2.1. The concept of force  1.2.2. newton's first law of motion  1.2.3. Newton's second law of motion  1.2.4. Newton's third law of motion  1.2.5. Inertia and types of inertia  1.2.6. Motion  1.2.7. Conservation of momentum  1.2.8. Application of Newton's laws in daily life  1.2.9. Types of Forces (Contact and Non-Contact)  1.2.10. Friction and its effects  1.3. Gravitational force  1.3.1. Newton's law of universal gravitation  1.3.2. Importance of Gravitational Force  1.3.3. Acceleration due to gravity  1.3.4. Free fall and weightlessness  1.3.5. Mass and weight  1.3.6. Variation of g with height and depth  1.3.7. Kepler's laws of planetary motion  1.3.8. Satellites and their orbits  1.4. Work, Energy and Power  1.4.1. Concept of work  1.4.2. Positive and negative actions  1.4.3. Work done by constant and variable force  1.4.4. Energy and its forms  1.4.5. Kinetic energy and potential energy  1.4.6. Law of conservation of energy  1.4.8. Commercial unit of energy  1.4.9. Work–energy theorem  1.5. Simple machines  1.5.1. Types of simple machines  1.5.2. Mechanical advantage  1.5.3. Machine efficiency  1.5.4. Levers and their types  1.5.5. Pulleys and Inclined Planes  1.5.6. Gears and their uses
  2. Properties of matter  2.1. States of matter  2.1.1. Solids, liquids and gases  2.1.2. Properties of different states of matter  2.1.3. Change in state of matter  2.1.4. Plasma and Bose–Einstein condensate  2.2. Density and pressure  2.2.1. Concept of density and relative density  2.2.2. Pressure in solids, liquids and gases  2.2.3. Pascal's law and its applications  2.2.4. Atmospheric pressure and its variations  2.2.5. Surface tension and capillarity  2.3. Buoyancy and Archimedes' principle  2.3.1. Buoyant force  2.3.2. Archimedes principle  2.3.3. Applications of Archimedes' Principle  2.3.4. floating and sinking objects  2.3.5. Theory of Flotation and Archimedes' Principle
  3. Heat and Thermodynamics  3.1. Temperature and heat  3.1.1. Concept of heat and temperature  3.1.2. Temperature measurement  3.1.3. Temperature scales  3.2. Heat transfer  3.2.1. Conduction of heat  3.2.2. Convection of heat  3.2.3. heat radiation  3.2.4. Applications of heat transfer  3.2.5. Thermal conductivity  3.3. Thermal expansion  3.3.1. Expansion of solids, liquids and gases  3.3.2. Abnormal expansion of water  3.3.3. Applications of Thermal Expansion  3.4. Specific heat capacity and latent heat  3.4.1. Concept of specific heat capacity  3.4.2. Measurement and applications of specific heat  3.4.3. Latent heat of fusion and vaporization  3.4.4. Heat Engines and Efficiency
  4. Waves and sound  4.1. Waves and their types  4.1.1. Mechanical and electromagnetic waves  4.1.2. Longitudinal and Transverse Waves  4.1.3. Properties of Waves  4.1.4. Wavelength, frequency and speed of the wave  4.1.5. Superimposition of waves  4.2. Sound waves  4.2.1. Nature and transmission of sound  4.2.2. Speed of sound in different mediums  4.2.3. Reflection of sound and echo  4.2.4. Sonar and ultrasound  4.2.5. Resonance and pulsation  4.3. Sound characteristics  4.3.1. Intensity, loudness and quality of sound  4.3.2. Doppler effect in sound
  5. Lighting and Optics  5.1. Reflection of light  5.1.1. Laws of reflection  5.1.2. Reflection from a plane mirror  5.1.3. Reflection from a spherical mirror  5.1.4. Image formation by concave and convex mirrors  5.1.5. Applications of Reflection  5.2. Refraction of light  5.2.1. Laws of refraction  5.2.2. Refractive index  5.2.3. Refraction through a glass slab  5.2.4. Refraction in water and air  5.2.5. Lenses and their types  5.2.6. Image formation by convex and concave lenses  5.2.7. Total internal reflection and its applications  5.3. Dispersion and scattering of light  5.3.1. Spectrum of white light  5.3.2. Prisms and Dispersion  5.3.3. Tyndall effect and blue sky
  6. Electricity and Magnetism  6.1. Electric charge and static electricity  6.1.1. The concept of electric charge  6.1.2. Charging by friction, contact and induction  6.1.3. Electroscope and its working  6.2. Current Electricity  6.2.1. The concept of electric current  6.2.2. Ohm's Law and Resistance  6.2.3. Factors affecting resistance  6.2.4. Series and Parallel Circuits  6.2.5. Heating effect of electric current  6.2.6. Electric power and energy  6.3. Magnetism  6.3.1. Natural and artificial magnets  6.3.2. Properties of magnets  6.3.3. Earth's magnetism  6.3.4. Magnetic field and field lines  6.3.5. Electromagnets and their applications
  7. Modern Physics  7.1. structure of the atom  7.1.1. Atomic Structure and Subatomic Particles  7.1.2. Electrons, Protons, and Neutrons  7.1.3. Rutherford and Bohr model  7.2. Radioactivity  7.2.1. Types of radioactive emissions  7.2.2. Half-life and radioactive decay  7.2.3. Uses and Hazards of Radioactivity
  8. Space science and astronomy  8.1. The universe and its components  8.1.1. Stars and galaxies  8.1.2. Planets and Solar System  8.2. Satellites  8.2.1. Natural and artificial satellites  8.2.2. Use of satellites

Grade 9 → Properties of matter → States of matter ↓


Solids, liquids and gases


States of matter are a fundamental concept in physics and chemistry that describe the different forms of different phases of matter. The three most common states are solid, liquid, and gas. They are characterized by their physical properties, including volume, shape, and the behavior of their particles.

Solids

Solids are substances with definite shape and volume. The particles in solids are packed very closely to each other, usually in a regular arrangement. Because of this close packing, the particles in a solid vibrate but do not move from their positions, allowing solids to keep their shape.

Common examples of solids include rocks, ice, and wood.

In the above figure we can see that the particles in a solid are tightly packed together in a structured pattern.

Liquids

Liquids have a fixed volume but take the shape of their container. Particles in liquids are adjacent to each other but not in a fixed position, causing them to pass one another. This gives liquids the ability to flow.

Examples of liquids include water, oil, and honey.

The particles in the above liquids are close together, but unlike solids, can move around each other.

Liquids have many interesting properties such as surface tension, viscosity and capillary action. Surface tension is the tendency of liquid surfaces to shrink to a minimum surface area. This is why small insects can walk on water without sinking.

Gases

Gases have neither a definite shape nor a definite volume. The particles of gases are in constant, random motion and are far apart from one another, making them easily compressible. This allows gases to fill any space or container they are in.

Some common examples of gases include air, carbon dioxide, and steam.

The above gas particles are far away from each other and are moving irregularly.

Comparison of solids, liquids and gases

  • Solid: definite shape and volume, particles vibrate in place.
  • Liquids: definite volume, take the shape of the vessel, particles can pass past each other.
  • Gases: They have no definite shape or volume, particles move freely and are at a great distance from each other.

Changes in state

Changes in temperature or pressure can cause substances to change from one state to another. When a solid substance is heated, its particles gain energy and begin to move more freely, causing it to turn into a liquid. This process is called melting. Conversely, when a liquid loses heat, it turns into a solid through a process called freezing.

When a liquid is heated, its particles move faster and eventually enter the gas state in a process called boiling or evaporation. Conversely, when a gas cools, it turns into a liquid in a process called condensation.

These are summarised below:

  • Melting: solid to liquid
  • Freezing: Liquid to Solid
  • Evaporation/Boiling: Liquid to Gas
  • Condensation: gas to liquid

Examples in nature

Consider the water cycle as an example of changing states of matter. Water evaporates from rivers, lakes and oceans to become water vapor, a gas. It then condenses in the atmosphere to form clouds (liquid) and eventually falls as precipitation (solid/liquid) such as rain, snow or hail and goes back into rivers and oceans.

Understanding the kinetic molecular theory

This theory explains the behaviour of particles in every state of matter:

  • In solids the particles vibrate at fixed locations.
  • In liquids the particles move around, but they still remain close to each other.
  • The particles in gases move around freely and are far apart from each other.

Density and states of matter

The density of a substance is defined as its mass per unit volume. Different states of matter have different densities because the distances between particles vary. For example, solids are generally denser than liquids, and liquids are denser than gases.

Density (ρ) = Mass (m) / Volume (V)

The units of density are usually kilograms per cubic metre (kg/m3).

Water is an interesting case, because ice (solid water) is less dense than liquid water. This is why ice floats on water.

Conclusion

Understanding solids, liquids and gases is important for understanding the nature of different substances and their behavior under different conditions. This basic knowledge forms the basis for more advanced topics in physics and chemistry, such as thermodynamics, fluid dynamics and materials science. Classifying substances into these three states helps us predict and control how substances will behave in different environments, which has applications in countless scientific and engineering fields.


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Solids, liquids and gases

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