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 → Heat and Thermodynamics → Thermal expansion ↓


Expansion of solids, liquids and gases


Thermal expansion is a fundamental concept in heat and thermodynamics that describes how the size of objects changes with temperature. All substances, whether solids, liquids or gases, expand when heated and contract when cooled. This principle is important in understanding many natural phenomena and has practical applications in engineering, construction and everyday life.

Basic concept of thermal expansion

When a substance is heated, its particles begin to move more vigorously. This increase in particle vibration causes the substance to expand. The degree of expansion depends on the original size of the substance, the temperature change occurring in it, and its coefficient of thermal expansion. This concept can be expressed by a simple formula:

ΔL = α × L₀ × ΔT

Where:

  • ΔL is the change in length of the object.
  • α is the specific linear expansion coefficient for the material.
  • L₀ is the original length of the object.
  • ΔT is the change in temperature.

Expansion of solids

Solids have a definite shape and volume, and their particles are very closely packed together. As a result, solids usually have the lowest thermal expansion coefficients compared to liquids and gases. Nevertheless, the expansion of solids is important and must be taken into account in many applications.

Examples of diffusion in solids

Railways: Railway tracks are made of steel and expand during summer. To accommodate this expansion, gaps, known as expansion joints, are deliberately left between the tracks.

Bridges: Metal bridges are designed with uniform expansion joints to prevent structural damage due to temperature changes throughout the year.

In the example above, the solid line might represent a metal rod at room temperature. When heated, the dashed line shows how the metal rod expands. You can visually see the increase in length.

Expansion of liquids

Liquids, though less constrained than solids, also expand when heated. Unlike solids, liquids have no fixed shape, allowing them to expand more freely. The expansion of liquids is measured as a change in volume rather than length.

The formula for volume expansion can be given as:

ΔV = β × V₀ × ΔT

Where:

  • ΔV is the change in volume.
  • β is the coefficient of volume expansion.
  • V₀ is the original volume of the liquid.

Examples of diffusion in liquids

Thermometer: A common example is a mercury thermometer. As the temperature increases, the mercury expands and rises in a thin column, making it possible to measure temperature.

Water bodies: During warm weather, the surface of lakes and oceans expands as temperatures rise. Although this is imperceptible on a small scale, it can affect local weather patterns.

In this visualization, the blue column shows liquid in a narrow container at two different temperatures. The shaded portions show how the liquid expands as the temperature increases, similar to how a liquid thermometer works.

Expansion of gases

Gases expand much more than solids and liquids when heated. This is because gas molecules are far apart and move freely, making the expansion more obvious. Following Charles's law, most gases expand at a constant rate with temperature when the pressure is held constant.

Charles's law states:

V₁/T₁ = V₂/T₂

This relation shows that when the pressure is constant the volume of a gas is directly proportional to its temperature.

Examples of expansion in gases

Hot air balloons: Hot air balloons rise because the air inside the balloon heats up, causing it to expand. The balloon floats because it has a lower density than the outside air.

Car tyres: In hot weather, the air inside car tyres expands, increasing the tyre pressure. Keeping an eye on tyre pressure is very important to avoid accidents.

The solid circle represents the gas at its initial temperature, and the dashed circle shows how much the gas expands as the temperature increases.

Applications of thermal expansion

Thermal expansion plays a vital role in various aspects of life:

Building and construction: Engineers must take thermal expansion into account when designing buildings, bridges and roads to prevent structural failures.

Household appliances: Appliances such as refrigerators and ovens depend on the coefficient of thermal expansion to function efficiently.

Cooking: Pans expand when heated. This expansion helps distribute the heat evenly, which cooks food more efficiently.

Pipes: Pipe systems must accommodate changes in length due to changes in temperature to prevent leakage and rupture.

Conclusion

Understanding thermal expansion is important to many areas of science and engineering. From steel beams in skyscrapers to airbags in cars, thermal expansion is a critical factor that affects the design and operation of many systems. By understanding the principles of how different materials expand with heat, engineers and scientists can create safer, more efficient designs. While the math of thermal expansion can seem daunting, the basic concept is simple: materials expand when heated and contract when cooled.


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Expansion of solids, liquids and gases

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