How sound travels through solids, liquids and gases, how the ear works and why hearing has limits, and distances from echoes.
What you will learn
- Explain how sound travels and why its speed depends on the material
- State the range of human hearing and why it is limited
- Calculate distances from echo times with s = v t
Vibrating particles
A sound wave is a longitudinal wave: particles vibrate back and forth along the direction the wave travels, passing the vibration on.
With no particles, as in space, there is no sound.
Sound is fastest in solids, slower in liquids and slowest in gases (about 330 m/s in air, 1500 m/s in water, around 5000 m/s in steel).
When sound passes into a new material its frequency stays the same (the source sets it). The speed changes, so by v = f λ the wavelength changes too.
The rest of this lesson and its 9 practice questions are locked.
In this lesson
- Vibrating particles
- The ear and its limits
- Echoes
- Try it: Your first echo
9 practice questions, marked as you go; about 25 minutes in all.
Key terms
Frequency stays the same, Ultrasound
In this unit: Lenses, visible light, sound and black bodies
Reflection and the glass block practical, total internal reflection and optical fibres, colour and filters, lenses and magnification, sound and echoes, ultrasound and seismic waves, and black body radiation (Physics only).