Track quiz
Show on a big screenThe nine rules first. Then the quiz.
| Idea | The rule |
|---|---|
| Something has to shake | Every sound is made by something that vibrates. Stop the vibration and the sound stops. |
| A medium | Sound needs a medium to travel through. It is usually fastest in solids, slower in liquids, slowest in gases. In a vacuum, no sound arrives. |
| What moves | A sound wave is a run of compressions and rarefactions. It travels through a medium. The pieces of the medium only shake about their own places. Energy travels, not the medium. |
| Loudness | A bigger amplitude means a louder sound and more energy. Loudness does not change how fast the sound travels. |
| Pitch | Frequency is the number of complete shakes in one second. Its unit is the hertz. A higher frequency is heard as a higher pitch. Frequency × time period = 1. |
| What we hear | People hear sounds from about 20 Hz to 20 000 Hz. A frequency below 20 Hz is infrasound. A frequency above 20 000 Hz is ultrasound. |
| Echo | A hard surface reflects sound. A return 0.1 s or more late is heard as an echo. The wall is half the round trip away. |
| Sonar | Sonar times an echo to find a distance under water. The pulse goes there and back. So the distance is half of speed × time. |
| Wavelength | Speed = wavelength × frequency, or v = λ × ν. In one medium at one temperature, a higher frequency gives a shorter wavelength. |
A bell rings. A hand touches the rim and the sound stops. Why?
A bell rings inside a jar. The air is pumped out. What do you hear?
A knock on a long steel rail. A friend far away hears it twice. Which sound comes first?
A sound crosses a room. What travels across?
A drum is hit harder. What gets bigger?
A string shakes 15 times in 3 s. What is its frequency?
A string is tightened. Its note goes higher. What went up?
A sound has a frequency of 10 Hz. What kind of sound is it?
An echo returns after 0.3 s. Sound travels at 340 m/s. How far is the wall?
A sonar pulse returns after 8 s. Water carries it at 1500 m/s. How deep is the sea?
Sound in air moves at 340 m/s. A wave has a wavelength of 5 m. What is its frequency?
This is Chapter 10 once more, Exploration — Sound Waves: Characteristics and Applications.
Next comes Reproduction: How Life Continues. A cell divides in two, and both carry the same instructions.
Reveal every answer to finish this lesson.