- Define and explain Echoes and Hearing in your own words
- Use key terms such as vibration accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
This lesson focuses on Echoes and Hearing: using echoes to find distances and seeing how the ear detects sound.
Using echoes to find distances and seeing how the ear detects sound.
Key ideas
Sounds are made by vibrations
Pluck a guitar string and it vibrates, pushing the air back and forth — that is what your ear detects as sound. The vibrating object can be a string, a drum skin, vocal cords or a loudspeaker cone. No vibration, no sound — it really is that simple.
Pitch depends on frequency, loudness on amplitude
Fast vibrations give a high frequency and a high-pitched note; slow vibrations give a low pitch. Big vibrations (large amplitude) make loud sounds, small ones make quiet sounds. Human hearing spans roughly 20 Hz to 20,000 Hz, and it fades at the top end as we age.
Key term — vibration: A rapid back-and-forth movement — the source of every sound.
A ship's sonar echo returns after 4 s. The speed of sound in water is 1500 m/s. How deep is the water?
Distance = 1500 × 4 ÷ 2 = 3000 m.
Answer: Distance = 1500 × 4 ÷ 2 = 3000 m.
- Thinking sound travels in space Sound needs a medium — with no particles in a vacuum, astronauts must use radios.
- Forgetting the echo travels there and back Echo timing covers double the distance, so you must halve speed × time.
Practice
Steel is faster: about 5000 m/s in steel versus about 343 m/s in air.
The pitch — hertz measures frequency, which determines pitch.
Space is a vacuum with no particles, so sound cannot travel between them — they use radios instead.
The drum skin (membrane) vibrates and pushes the air back and forth.
Quick check
Which of these best defines "vibration"?
Tightening a guitar string raises the note. Why?
- Echoes and Hearing: using echoes to find distances and seeing how the ear detects sound.
- Sounds are made by vibrations: Pluck a guitar string and it vibrates, pushing the air back and forth — that is what your ear detects as sound.
- amplitude: The size of a vibration; a bigger amplitude means a louder sound.
- Watch out for: thinking sound travels in space