Grade 7
  1. Introduction to Physics  1.1. Definition and scope of physics  1.2. Importance of Physics in Daily Life and Technology  1.3. Scientific method and its applications in physics  1.4. Measurement and Experiments in Physics  1.5. Branches of Physics and their Applications  1.6. Relation of physics with other sciences
  2. Measurement and units  2.1. Fundamental and derived quantities  2.2. SI units and unit conversions  2.3. Length measuring instruments and tools used  2.4. Measuring the difference between mass and weight  2.5. Measuring time with accuracy  2.6. Measuring the Volume of Regular and Irregular Objects  2.7. Measuring Temperature and Temperature Scales  2.8. Accuracy, Precision, and Significant Figures  2.9. Errors in Measurement and How to Reduce Them  2.10. Estimates and approximations in scientific calculations  2.11. Standard form and order of magnitude
  3. Speed and Force  3.1. Introduction to motion and rest  3.2. Types of motion - uniform and non-uniform  3.3. Scalars and vectors in motion  3.4. Speed, Velocity, and Acceleration  3.5. Distance-time and velocity-time graphs  3.6. Newton's first law of motion (law of inertia)  3.7. Newton's second law of motion (force and acceleration)  3.8. newton's third law of motion  3.9. Types of forces - contact and non-contact forces  3.10. Effect of forces on motion  3.11. Friction – types, effects and applications  3.12. Gravity, free fall and gravitational acceleration  3.13. Circular motion and centripetal force  3.14. Application of Newton's laws in real life
  4. Energy, Work and Power  4.1. Definition and forms of energy  4.2. Potential and Kinetic Energy  4.3. Law of conservation of energy  4.4. Energy transformations in everyday life  4.5. Work done by force and its calculation  4.6. Power - Definition and Calculation  4.7. Simple Machines and Mechanical Advantage  4.8. Efficiency and energy losses of machines  4.9. Renewable and non-renewable energy sources
  5. Heat and temperature  5.1. Difference Between Heat and Temperature  5.2. Thermometer and temperature scale (Celsius, Kelvin, Fahrenheit)  5.3. Expansion and contraction of solids, liquids and gases  5.4. Heat transfer methods – conduction, convection and radiation  5.5. good and bad conductors of heat  5.6. Applications of heat transfer in daily life  5.7. Specific heat capacity and its applications  5.8. Latent heat and change of state  5.9. Thermal equilibrium and heat exchange  5.10. effect of heat on matter
  6. Lighting and Optics  6.1. Nature and properties of light  6.2. Reflection of light and laws of reflection  6.3. Image formation by plane and curved mirrors  6.4. Refraction of light and the laws of refraction  6.5. Lenses – convex and concave, image formation  6.6. Optical instruments – microscope, telescope, camera  6.7. Dispersion of light and formation of spectrum  6.8. Human eye, vision defects and their correction  6.9. Applications of optics in daily life  6.10. Total internal reflection and its applications
  7. Sound and waves  7.1. Nature and properties of waves  7.2. Production and propagation of sound  7.3. Characteristics of sound waves – frequency, amplitude, wavelength  7.4. Speed of sound in different mediums  7.5. Reflection of sound – echo and reverberation  7.6. Ultrasound and its applications  7.7. Doppler effect in sound waves  7.8. Noise pollution and its effects  7.9. Applications of sound in medicine and industry
  8. Electricity and Magnetism  8.1. Electric charge and static electricity  8.2. Electrical conductors and insulators  8.3. Electric current, voltage and resistance  8.4. Ohm's law and its applications  8.5. Electrical Circuits - Series and Parallel Circuits  8.6. Electric power and energy consumption  8.7. Safety precautions in the use of electricity  8.8. Properties of magnets and magnetic fields  8.9. Electromagnets - How They Work and Their Uses  8.10. Relation between electricity and magnetism (electromagnetic induction)  8.11. Applications of electromagnetism in technology  8.12. Earth's magnetic field and its effects
  9. Matter and its properties  9.1. Classification of matter- solid, liquid and gas  9.2. Properties of different states of matter  9.3. Kinetic theory of matter  9.4. Changes in the state of matter and their causes  9.5. Expansion and contraction of substances  9.6. Density and its calculation  9.7. Pressure in solids, liquids and gases  9.8. Atmospheric pressure and its effects  9.9. Applications of pressure in daily life  9.10. Buoyancy and Archimedes' principle
  10. Space Science and Solar System  10.1. Introduction to Astronomy  10.2. Solar System - Planets and their Characteristics  10.3. Sun - structure and energy production  10.4. Moon - phases and its effect on Earth  10.5. Rotation and revolution of the earth  10.6. Solar and lunar eclipses  10.7. Gravity in space and its role in orbits  10.8. Artificial satellites and their uses  10.9. Space exploration and modern discoveries  10.10. Asteroids, comets and meteors  10.11. Life beyond Earth - Possibilities and Theories
  11. Environmental Physics  11.1. Impact of physics on environmental science  11.2. Renewable and non-renewable energy sources  11.3. Energy conservation and efficiency  11.4. Climate change and its effects on Earth  11.5. Air, water and soil pollution – causes and effects  11.6. Greenhouse effect and global warming  11.7. Sustainable development and environmental protection  11.8. Role of Physics in Weather and Climate Studies

Grade 7 → Sound and waves ↓


Speed of sound in different mediums


The speed of sound is one of the most fascinating concepts in physics. It involves understanding how sound travels through different substances or mediums. The speed of sound waves largely depends on the medium they are traveling through. Let's explore this concept in detail!

What is sound?

Before learning about the speed of sound, it is important to understand what sound actually is. Sound is a form of energy that travels in the form of waves. These waves are created when an object vibrates, causing the air molecules around it to vibrate. These vibrations travel through the air in the form of sound waves, which are eventually detected by our ears.

How do sound waves travel?

Sound travels in wave patterns, much like the ripples created when a stone is thrown into a pond. Here's a simplified representation of sound waves:

In the figure above, the line represents the oscillation path of a sound wave. The speed of these waves can vary depending on the medium they travel through.

What is the medium?

The medium is the substance or material that carries sound waves. Gases, liquids, and solids can all act as a medium that carries sound. However, each of these mediums has different properties that affect the speed at which sound travels through them.

Why is the speed of sound different in different mediums?

The speed of sound in different mediums varies due to two main factors: the density and elasticity of the medium. Let's break these down:

  • Density: This is the mass of a substance per unit volume. In general, sound travels faster in denser media.
  • Elasticity: This describes how quickly a material returns to its original shape after being deformed. More elastic materials help sound travel faster.

Speed of sound in air

Sound travels in air at a speed of about 343 meters per second (at 20 degrees Celsius). In air, the speed of sound can vary depending on temperature, humidity, and pressure.

Example

Imagine you are standing 343 meters away from your friend. You both decide to clap together. How long will it take for the sound of the claps to reach each other? Since the speed of sound in air is 343 m/s, it will take exactly 1 second for the sound to travel that distance.

Speed of sound in water

Sound travels very fast in water, about 1482 meters per second. This is because water is denser and more flexible than air.

In our picture you can see that sound waves in water follow the same path as sound waves in air, but they travel much faster.

Example

You are swimming underwater and hear a boat horn from 1482 m away. This sound will reach you in about 1 second because the speed of sound underwater is 1482 m/s.

Speed of sound in solids

Solids carry sound waves even faster than liquids and gases. For example, the speed of sound in steel is about 5960 meters per second.

In the figure, a sound wave in a solid medium is shown traveling faster and with more energy than in air or water.

Example

You tap a steel railing with a hammer. A person standing 596 m away will hear the tap exactly 0.1 s later, because the speed of sound in steel is 5960 m/s.

Formula for speed of sound

The speed of sound is given by the following formula:

v = √(E/ρ)

Where:

  • v is the speed of sound in the medium (m/s)
  • E is the elasticity of the medium
  • ρ is the density of the medium (kg/m^3)

This formula summarizes how the speed of sound depends on the elastic and dense properties of the medium. Solids, being very elastic and generally dense, provide the fastest path for sound waves, while gases with low density and elasticity provide the slowest speed.

Factors affecting the speed of sound

Temperature

The speed of sound in air increases as the temperature increases. Higher temperatures cause air molecules to move more quickly, speeding up the propagation of sound waves.

Pressure and humidity

Although pressure has little effect on the speed of sound in air, high humidity (more water vapor in the air) can increase the speed of sound, because water vapor is less dense than dry air.

Applications in daily life

Understanding the speed of sound has practical applications, such as in ultrasound imaging used in medical examinations. Ultrasound equipment uses sound waves that travel much faster through tissues and fluids than through air to create images of the inside of the body.

In engineering, knowing how sound travels through different materials helps design buildings and vehicles to effectively control noise.

Conclusion

The speed of sound depends on the medium it travels through. By exploring the principles of density and elasticity, we gain insight into why sound moves the way it does through air, water, and solids. This knowledge not only enriches our understanding of sound and waves, but also plays a vital role in technological advancements and everyday applications.


Grade 7 → 7.4


U
username
0%
completed in Grade 7

← Prev (7.3)
Characteristics of sound waves – frequency, amplitude, wavelength
Next (7.5) →
Reflection of sound – echo and reverberation

Comments 



Speed of sound in different mediums

https://www.physicsflow.com/g7/7.4?pfal=en