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How does sound travel from one place to another?

Class 9 ScienceNCERT chapter: Soundइसे हिंदी में पढ़ें

Exam-ready answer

Sound travels from one place to another as a mechanical wave through a medium (solid, liquid or gas). When an object vibrates, it pushes nearby particles, creating regions of compression and rarefaction. These disturbances travel through the medium without the particles themselves moving from one place to another.

Explanation

Sound is produced by vibrating objects. When a body vibrates, it pushes the particles of the surrounding medium, creating a region of high pressure called compression. When it moves back, it creates a region of low pressure called rarefaction. This cycle repeats, and the disturbance travels through the medium as a wave.

The particles of the medium do not travel from the source to the listener; they only vibrate about their mean positions. The energy of the vibration is passed from one particle to the next. This is why sound needs a material medium—solid, liquid or gas—to travel. It cannot travel through vacuum.

For example, when a tuning fork vibrates, it sets the air particles around it into vibration, producing compressions and rarefactions. These reach our ears as sound. Similarly, sound travels faster in solids than in liquids and gases because the particles are closer together.

Points to remember

  1. Sound is a mechanical wave that requires a medium (solid, liquid or gas) to travel.
  2. It propagates as compressions and rarefactions in the medium.
  3. Particles of the medium vibrate about their mean positions but do not move from one place to another.
  4. Sound cannot travel through vacuum.
  5. Speed of sound: solids > liquids > gases (e.g., in air at 25°C, speed ≈ 346 m/s).

Exam tip

Draw a labelled diagram showing compressions and rarefactions in a sound wave. Mention that sound needs a medium and cannot travel in vacuum.

Questions students also ask

Why can't sound travel in vacuum?
Sound needs a material medium to propagate because it travels by the vibration of particles. In vacuum, there are no particles to vibrate and carry the disturbance, so sound cannot travel.
What are compression and rarefaction?
Compression is a region of high pressure and high particle density in a sound wave. Rarefaction is a region of low pressure and low particle density. They alternate as the wave moves through the medium.
Does sound travel faster in solids or gases?
Sound travels faster in solids than in gases because the particles in solids are closely packed, allowing faster transfer of energy. For example, speed of sound in steel is much higher than in air.

Chapter labels help you find the topic in your textbook. Check your own edition: chapter names and order can change. These are Know.it explanations, not official NCERT solutions.