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


Thermal expansion is a concept in the branch of physics known as thermodynamics, which deals with the relationship between heat, temperature, and energy. It describes the tendency of matter to change its shape, area, volume, and density in response to changes in temperature. In simple terms, when substances are heated, they expand, and when they are cooled, they contract. This behavior is observed in solids, liquids, and gases, although in different ways.

What causes thermal expansion?

At the atomic level, thermal expansion occurs because atoms and molecules vibrate more at higher temperatures. As the temperature of a substance increases, these particles move more rapidly, pushing each other further apart. This increase in speed and separation results in the expansion of the substance.

Example 1: Iron rails on a hot day

During the summer, you may notice that train tracks sometimes warp or bend. This happens because metal tracks expand as temperatures rise. Engineers accommodate this expansion by leaving small gaps, called expansion joints, between rail sections.

Types of thermal expansion

There are generally three types of thermal expansion that are important to consider: linear expansion, area expansion, and volume expansion. Each type describes how different dimensions of materials can expand due to changes in temperature.

1. Linear expansion

Linear expansion refers to the change in one dimension (length) of an object when it is heated or cooled. It is usually seen in long objects such as rods and rails. The change in length can be calculated by the formula:

 ΔL = αL₀ΔT

Where:

  • ΔL is the change in length
  • α (alpha) is the coefficient of linear expansion
  • L₀ is the original length
  • ΔT is the change in temperature
L₀ L₀ + ΔL

Example 2: A metal rod

Consider a metal rod that is 2 m long. If its coefficient of linear expansion is 12 × 10 -6 per degree Celsius, and the temperature rises by 30 °C, the change in length can be calculated as:

 ΔL = 12 × 10^-6 × 2 × 30 = 0.00072 m or 0.72 mm

2. Area expansion

For objects that have a large surface area, such as sheets or plates, area expansion is considered. The formula for area expansion can be given as:

 ΔA = 2αA₀ΔT

Where:

  • ΔA is the change in area
  • A₀ is the fundamental region
A₀ A₀ + ΔA

3. Volume expansion

Volume expansion is the most commonly observed type of expansion, especially in fluids. It describes how the entire volume of an object expands. The formula for volume expansion is:

 ΔV = βV₀ΔT

Where:

  • ΔV is the change in volume
  • β (beta) is the coefficient of volume expansion, which for solids is usually about 3α
  • V₀ is the original volume
V₀ V₀ + ΔV

Example 3: Balloon in the sun

Imagine a balloon filled with air. When you release it into the sun, the air inside heats up, causing the balloon to expand. This is volume expansion in action. If you have to measure the change in volume, you can use the above formula to calculate the expansion based on the initial volume and the temperature change.

Applications of thermal expansion

Bridges

Many bridges have expansion joints that allow them to expand and contract with temperature changes without causing structural damage.

Thermal expansion in liquid thermometer

Liquid thermometers, such as those containing mercury or alcohol, rely on thermal expansion. As the temperature rises, the liquid expands and rises in the narrow tube, indicating the temperature.

Power lines

Power lines are often loosely strung between poles to allow thermal expansion in the summer without breaking. In the winter, they shrink and become even tighter due to the cold.

Conclusion

Thermal expansion plays a key role in many everyday phenomena and technological applications. Understanding how materials expand and contract with changes in temperature is essential for designing safe and effective structures, devices, and systems. By considering the coefficients of expansion for different materials, engineers and scientists can anticipate and mitigate potential problems caused by temperature fluctuations.


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Thermal expansion

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