How Sound Travels Notes & Questions | Class 5 Physics | Drishti OS

How Sound Travels

What you'll learn

Sound needs a medium — a solid, liquid, or gas — to travel; it cannot travel through empty space (vacuum).
Sound travels fastest through solids, slower through liquids, and slowest through air (gases).
Putting your ear on a railway track can let you hear an approaching train's sound through the solid track before you hear it through the air.
Sound travels through air at roughly 340 metres every second, which is much slower than light.
An echo is heard when sound reflects off a hard, distant surface (like a wall or a hill) and returns to our ears a little later.

Key concepts

Level 1 - Core idea

Verbal: Sound needs a medium such as a solid, liquid, or gas to travel, and cannot travel through a vacuum. It travels fastest through solids and slowest through air, and can reflect off hard surfaces to produce an echo.

Symbolic: sound + medium (solid/liquid/gas) -> travels; sound + vacuum -> cannot travel

Visual: Shout toward a large hill or wall far away and you may hear your own voice come back to you a moment later as an echo.

Level 2 - NCERT anchor

NCERT Looking Around 5 connects this to real-life examples like hearing a distant train through railway tracks and hearing echoes in large empty halls.

Worked example

Why can astronauts in outer space not talk to each other directly through the air outside their spacesuits?

Step 1 - Outer space is mostly empty, a vacuum with no air.
Step 2 - Sound needs a medium like air, water, or a solid to travel.
Step 3 - With no medium outside, sound cannot travel through space.
Answer: Sound cannot travel through the vacuum of space, so astronauts use radios instead.

Why might you hear an approaching train through a railway track before you hear it through the air?

Step 1 - Sound travels faster through solids than through air.
Step 2 - The metal track is a solid medium touching the ground.
Step 3 - Sound through the track reaches your ear sooner than through air.
Answer: Sound reaches you faster through the solid track than through the air.

Common mistakes

Mistake	Why it happens	Fix
Thinking sound can travel through empty space	Confusing sound with light, which can travel through vacuum	Sound needs a medium and cannot travel through a vacuum, unlike light
Thinking sound travels fastest through air	Not knowing solids conduct sound faster	Sound actually travels fastest through solids, slower through liquids, slowest through air
Thinking an echo and the original sound are heard at the exact same instant	Ignoring the time needed for sound to travel and return	An echo is heard a little later because the sound must travel to a surface and reflect back
Thinking sound travels instantly, with no speed at all	Assuming sound has no travel time	Sound travels at a definite speed, roughly 340 metres per second in air

Quick check

What does sound need in order to travel from one place to another?
Through which state of matter does sound travel fastest?
Why can sound not travel through outer space?
What is an echo?
Stretch: Why might a big empty hall produce a clearer echo than a small room full of curtains and furniture?

Revision tip: Recall: no air, water, or solid around you means no sound can travel to your ears.

Open the Practice tab for graded questions on How Sound Travels.

How Sound Travels