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 ↓


Resonance and pulsation


Sound waves are a fascinating phenomenon of physics that allows us to experience the world through our auditory senses. In this detailed explanation, we will delve deep into two interesting aspects of sound: resonance and pulsation. By breaking down these concepts into simpler parts, and with examples, you will gain a comprehensive understanding of how sound behaves under different circumstances.

Understanding sound waves

To understand resonance and beats, we must first understand what sound waves are. Sound is a type of wave that is created by vibrating objects and travels through a medium, usually air. Sound waves are longitudinal waves, which means that the direction of vibration of the particles in the medium is parallel to the direction of wave propagation.

The concept of frequency

Frequency, measured in Hertz (Hz), is the number of waves that pass a point in one second. This is an essential factor because it determines the pitch of a sound. High-frequency sounds have a high pitch, while low-frequency sounds have a low pitch.

What is resonance?

Resonance occurs when an object vibrates at its natural frequency due to an external stimulus. This can amplify the vibration substantially. For example, when you push someone on a swing, you naturally time your pushes to match the natural frequency of the swing. When the timing is just right, even small pushes can make the swing move higher. This is resonance.

Mathematically, resonance occurs when the frequency of the driving force matches the natural frequency of the system. Consider a simple mathematical relationship:

    F_ext = F_nat
    F_ext = F_nat

Where F_ext is the external frequency and F_nat is the natural frequency.

Real life examples of resonance

  • Musical instruments: A guitar string vibrates when plucked. If other strings are tuned to the same frequency, they can also vibrate.
  • Bridges: Soldiers are often instructed to break their pace when moving across a bridge, to prevent resonance vibrations, which can destabilize the structure.
Bridge Frequency wave

Pulsations in sound waves

Beats occur when two waves of slightly different frequencies interfere with each other. This interference causes a new wave pattern where the amplitude of the sound appears to oscillate or "beat". These beats can be heard as variations in the loudness of the sound.

The beat frequency is the difference between the frequencies of two interfering sound waves. If the frequency of wave 1 is f 1 and the frequency of wave 2 is f 2, then the beat frequency f beat is given by:

    f beat = |f 1 - f 2 |
    f beat = |f 1 - f 2 |

Example of beats

Imagine you are tuning a musical instrument by ear. If two notes are close in frequency, you will hear a beat. The musician then adjusts the tension in the strings until the beat disappears, indicating that the two notes are in harmony.

Frequency 1 Frequency 2

Interference and superposition principle

Beats are a product of the interference of sound waves. Interference occurs when two waves meet and combine. The superposition principle states that at any point, the resultant wave displacement is the sum of the displacements of the individual waves. There are two main types of interference:

  • Constructive interference: This occurs when wave peaks meet, causing the amplitude to increase.
  • Destructive interference: This occurs when the peaks and troughs meet, causing the amplitude to decrease.

Applications of beets

Beats are not just an interesting phenomenon; they also have practical applications. For example, beats are used to:

  • Tuning musical instruments: Musicians use percussion to tune their instruments to desired frequencies.
  • Radio technology: Beats help tune the radio by adjusting to the exact frequency of a station.

Conclusion

Resonance and pulsation are fascinating aspects of sound waves that reflect the complex and beautiful nature of physics in everyday life. Understanding these concepts increases our understanding of sound and its applications in various fields. By exploring resonance and pulsation, we have also understood basic principles such as frequency, interference, and the importance of wave phenomena in our world.


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Resonance and pulsation

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