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 → Waves and sound → Sound waves ↓


Speed of sound in different mediums


Sound is a type of wave that travels through different materials. The speed at which sound travels can change depending on the material it is passing through. This is because different materials have different properties that affect the speed of sound waves. In this detailed explanation, we are going to explore how sound travels through different mediums, including air, water, and solids. Let's start by understanding some basic concepts about sound and its propagation.

What are sound waves?

Sound waves are a type of mechanical wave. This means they require a medium such as air, water or a solid to travel. Sound waves are created when a source vibrates, causing the particles of the medium to vibrate as well. These vibrations pass through the medium in the form of compressions and rarefactions, which we perceive as sound.

How is the speed of sound calculated?

The speed of sound is determined by the medium through which it travels. The general formula used to calculate the speed of sound in a medium is:

c = sqrt(K/ρ)

Where:

  • c is the speed of sound.
  • K is the bulk modulus of the medium (a measure of how incompressible a medium is).
  • ρ (rho) is the density of the medium.

Speed of sound in air

Air is the most common medium through which sound travels, especially for humans. The speed of sound in air at room temperature (20 °C or 68 °F) is about 343 metres per second (m/s). Temperature and humidity can affect this speed. As the temperature increases, the speed of sound in air also increases.

Visual example of sound transmission in air

sound wave moves to the right in air

As shown above, the circles represent areas of compression by the sound source, and the distance between them represents how the wave travels through the air. This speed will change with factors such as temperature and humidity.

Speed of sound in water

Water is denser than air, which affects how sound travels through it. The speed of sound in water is about 1,480 m/s, which is much faster than in air. The high speed in water is due to water's stronger intermolecular forces and greater density than in air.

Text example

Imagine that you drop a stone into a pond. The splash creates waves that spread rapidly across the surface. If you could listen underwater, you would find that sound travels much faster through the water than it does above the surface to reach your ears.

Visual example of sound transmission in water

sound waves travel faster in water

In this illustration, the circles are closer together in water than in air, which shows the faster velocity of sound.

Speed of sound in solids

Sound travels fastest in solids because the particles in solids are more tightly packed than in liquids and gases. The speed of sound in a typical solid such as steel can reach 5,960 m/s. Solids have both elasticity and density that favor sound transmission:

Visual example of sound transmission in solids

Sound waves travel fastest through steel

Notice in the figure above how the circles are closest to each other in the representation of sound traveling through a solid medium. This represents the sound traveling at the highest speed among the other mediums.

Factors affecting the speed of sound

The speed of sound within a medium is affected by several major factors:

  • Density: Denser materials transmit sound faster, but this relationship is complicated by elasticity.
  • Elasticity: It is the ability of a material to return to its original shape, with more elastic materials conducting sound faster.
  • Temperature: Higher temperatures increase the speed of sound within gases because gases expand, decreasing density and increasing interactions between molecules.

Comparison of the speed of sound in different media

Here's a simple way to understand comparative speed:

Medium      | Approximate Speed (m/s)
-----------------------------------------
Air         | 343
Fresh Water | 1,480
Salt Water  | 1,530
Wood        | 3,850
Steel       | 5,960

Each medium has its own individual characteristics that determine how quickly sound waves travel through them. This summary shows that sound travels fastest in solids, slowest in liquids, and slowest in gases.

Practical examples in daily life

Understanding how the speed of sound changes is important in many everyday activities:

  • In nature: Lightning and thunder often provide a practical example. Light travels faster than sound; therefore, we see lightning before we hear thunder. Counting the seconds between lightning and thunder can help estimate the distance to a storm.
  • In communications: Early studies on sound helped improve telecommunications. Knowing the speed of sound helps in underwater communications, such as sonar technology used by submarines.
  • In music: The movement of sound enables musical instruments to work. For example, a guitar uses the vibration of air, while a xylophone has solid rods that vibrate to produce sound.

Conclusion

Exploring how sound travels through different mediums explains much about the energy and physics in our world. By investigating the principles that govern the velocity of sound in air, water, and solids, we gain scientific insights into both nature and technology. Understanding the speed of sound enriches our awareness and appreciation of the environment and the devices we use, which continues to inspire innovations and everyday applications.


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Nature and transmission of sound
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Speed of sound in different mediums

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