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 ↓


Buoyancy and Archimedes' principle


Buoyancy and Archimedes' principle are fundamental concepts in physics that explain how and why objects float or sink when placed in a fluid, whether it's a liquid or a gas. Understanding these concepts is important to explain phenomena that occur in everyday life, such as how ships float and why balloons fly in the sky.

Understanding the surge

Buoyancy is the upward force exerted by a fluid that opposes the weight of an object immersed in it. This force is what makes objects feel lighter in water and some objects float. Buoyancy is caused by pressure differences within the fluid, where pressure increases with depth.

Discovery of Archimedes' principle

Archimedes' principle is named after the ancient Greek mathematician and physicist Archimedes, who first discovered this principle. It states that any object fully or partially immersed in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces. This principle helps us determine whether an object will float or sink.

Formula of the principle of Archimedes

Buoyant force = weight of displaced fluid

Mathematical expression

The buoyancy force, F_b, is given by:

F_b = ρ_f × V_d × g

Where:

  • ρ_f (rho_f) is the density of the fluid.
  • V_d is the volume of the fluid displaced.
  • g is the acceleration due to gravity.

Visual example: floating object

buoyant force

In this example, the blue circle represents the object submerged in water, and the green arrow represents the buoyancy force acting upward.

Example 1: Floating log

Consider a wooden log floating on water. Its weight is exactly balanced by the buoyancy force, which is why it floats. The log displaces a certain amount of water, and according to Archimedes' principle, the buoyancy force is equal to the weight of this displaced water.

Example 2: Sinking of a stone

Now take a stone immersed in water. It sinks because the weight of the stone is more than the buoyancy force. Although the stone displaces some water, the buoyancy force is not enough to bear its weight. Therefore, it sinks.

Factors affecting buoyancy

  • Density of the fluid: The denser the fluid, the greater the buoyancy force. This is why objects float more easily in salt water than in fresh water.
  • Volume of displaced fluid: Greater is the volume of displaced fluid, hence greater is the buoyancy force.

Real-life applications of Archimedes' principle

Ships and submarines

Ships are designed to displace large amounts of water so that buoyancy forces keep them afloat. Submarines control buoyancy by adjusting ballast tanks to submerge or surface as needed.

Balloons and airplanes

Hot air balloons rise because the warm air inside is less dense than the cold air outside, creating a buoyant force. Similarly, helium balloons float because helium is less dense than air.

Buoyancy force calculation

Example calculation

Consider a cube with a side of 0.5 m that is completely submerged in water. Assuming the density of water to be (1000 , text{kg/m}^3), calculate the buoyancy force.

Volume of the cube = side × side × side = 0.5 m × 0.5 m × 0.5 m = 0.125 m³
    
Buoyancy force = ρ_f × V_d × g
F_b = 1000 , text{kg/m³} × 0.125 , text{m³} × 9.81 , text{m/s²}
f_b = 1226.25 , text{n}

A buoyancy force of 1226.25 newtons acts on the cube.

Summary

In short, buoyancy is an important concept in physics that explains why objects can float or sink in fluids. Archimedes' principle gives us a way to calculate the buoyancy force acting on an object, which is important for many practical applications, including shipbuilding, the design of submarines, and the use of balloons and airplanes. Understanding these principles not only helps us understand physical phenomena but also aids technological advancement.


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Buoyancy and Archimedes' principle

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