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 ↓


Archimedes principle


Archimedes' principle is a fundamental scientific law in physics, named after the ancient Greek mathematician and inventor Archimedes. The principle is a cornerstone in the study of fluid mechanics, particularly in understanding buoyancy, the phenomenon that makes an object float or sink in a fluid. Archimedes' principle states that any object, fully or partially submerged in a fluid, is lifted up by a force equal to the weight of the fluid displaced by the object.

Understanding the surge

To understand Archimedes' principle, we must first understand the concept of buoyancy. Buoyancy is the upward force exerted by a fluid on an object placed in it. This force allows objects to float, sink, or remain suspended in a fluid. For example, a boat floats on water because of buoyancy, while a stone can sink because the gravitational force pulling it down is greater than the buoyancy force pushing it upward.

Illustration of Archimedes' principle

Liquids object weight buoyant force

In the visualization above, you can see an object submerged in a fluid. The weight shown by the red arrow is the force that gravity exerts on the object. The orange arrow shows the buoyancy force pushing the object upward. According to Archimedes' principle, the orange arrow (buoyancy force) is equal to the weight of the fluid displaced by the green object.

Archimedes principle implemented

Let's take a closer look at how Archimedes' principle works in the real world:

Ambulatory

Objects float when the buoyancy force is equal to or greater than their weight. For example, a piece of wood floats on water because wood is generally less dense than water. The wood displaces an amount of water equal to its weight before it completely sinks, which is why it floats.

Density of Wood < Density of Water
Weight of Displaced Water = Weight of Wood

Drowning

An object sinks when its weight is greater than the buoyancy force. For example, a metal ball usually sinks in water because the density of metal is greater than the density of water. The weight of the displaced water is less than the weight of the ball.

Density of Metal > Density of Water
Weight of Displaced Water < Weight of Metal Ball

Suspension

An object is suspended when it is neither sinking nor floating. This occurs when the density of an object is equal to the density of the fluid. An example of this is a fish that can control its buoyancy and stay suspended in the water at a certain depth.

Density of Object = Density of Fluid

Archimedes principle in the properties of matter

Archimedes' principle doesn't just explain buoyancy; it also sheds light on the properties of matter, particularly in terms of density and volume. Density is a measure of how much mass is contained in a given volume. It is an essential property that affects whether an object will float or sink in a fluid.

Density

The formula to calculate the density is:

Density (ρ) = Mass (m) / Volume (V)

The symbol "ρ" (rho) represents density. Substances with a greater density than the liquid tend to sink, while substances with a lower density tend to float.

Volume and displacement

When an object is immersed in a fluid, it displaces a volume of that fluid. According to Archimedes' principle, the volume of the displaced fluid is directly related to the buoyant force. It can be expressed as:

Buoyant Force = Density of Fluid * Gravity * Displaced Volume

where gravity represents the acceleration due to gravity, which is about 9.8 m/s² at the Earth's surface.

Calculating with Archimedes' principle

Let's look at an example of how to use Archimedes' principle to calculate whether an object will float or sink:

Example problem

A cube with a density of 0.6 g/cm³ and a volume of 100 cm³ is placed in water. Will it float or sink?

Solution:

  1. Find the weight of the cube: 
    Weight = Density * Volume * Gravity = 0.6 g/cm³ * 100 cm³ * 9.8 m/s² = 588 grams-force
  2. Since the density of the cube (0.6 g/cm³) is less than the density of water (1 g/cm³), the cube displaces 100 cm³ of water.
  3. Calculate the buoyancy force: 
    Buoyant Force = Density of water * Volume of water displaced * Gravity = 1 g/cm³ * 100 cm³ * 9.8 m/s² = 980 grams-force

Since the buoyancy force (980 g-force) is greater than the weight of the cube (588 g-force), the cube will float.

Applications of Archimedes' principle

Archimedes' principle has applications in a variety of fields and technologies:

Ship design

Engineers design ships using Archimedes' principle to ensure that they float. By creating a hull shape that displaces enough water to balance the ship's weight, this ensures that the ship stays afloat.

Submarines

Submarines can float or sink by adjusting their buoyancy. They have ballast tanks that can be filled with air or water. When the tanks are filled with water, the submarine becomes denser and sinks. Conversely, when the tanks are filled with air, the submarine becomes less dense and rises.

Hot air balloon

This principle also applies to gases, though not liquids. Hot air balloons rise because the air inside the balloon heats up, making it less dense than the cold air outside. The buoyancy force acts upward, causing the balloon to float in the air.

Conclusion

Archimedes' principle is a simple but powerful concept that explains why objects float or sink. It is a fundamental principle used in many aspects of science and engineering. Understanding it not only helps us appreciate the wonders of physics, but also guides the application of these principles in the real world, impacting our understanding of technology, transportation, and nature.


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Archimedes principle

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