← ⚛️ Physics · usually met in Std 6-10
A travelling squeeze and stretch of the air. It needs something to travel through, which is why space is silent.
Something vibrates — a string, a drum skin, your vocal folds — and pushes the air next to it, which pushes the air next to that. The result is a wave of compressions and rarefactions moving outwards. Frequency, the number of vibrations a second, is heard as pitch; amplitude is heard as loudness. Unlike light, sound cannot cross a vacuum, because there is nothing there to be squeezed.
It travels faster through denser materials, not slower as most people guess: roughly 343 metres per second in air, about four times that in water, and faster still in steel. An echo is sound reflected back from a surface, and the time it takes to return can be used to measure distance — which is what bats, submarines and the ultrasound machine in a hospital all do.
Want to see it moving? Search YouTube for “Sound” ↗ — we send you to the search rather than to one video, because a link to one video eventually rots.
This entry was written for Star Student in our own words — it is a summary, not a source. Here is where the people who actually hold these facts keep them. Go and check.
Your own textbook ↗Balbharati publishes the textbooks free to read online. Your chapter is the thing to check first — an encyclopedia is a summary, and the syllabus is the syllabus.Last gone through: 1 October 2026 · How these entries are written
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