Chapter 14 – Sound
Consider the following statements and click to reveal the answer.
1. What happens to the vocal chords in the voice box when you whisper?
The whispering sound is made by vibrating the air in the throat so it cannot be felt by fingers on the voice box. The vocal chords do not play a part in making the sound.
2. On an oscilloscope:
- What would the display show for a loud high-pitched whistle?
- What kind of sound would make a display that showed low and well-spaced-out waves?
- The display would show tall ‘waves’ packed closely together.
- The sound would be quiet and of a low pitch – such as the hum you hear in a car as it travels along the road.
3. If there was a large explosion in outer space near to our planet, what would we see and what would we hear?
We would see a flash of light but we would not hear a sound because sound cannot travel through the vacuum in space.
4. What is the amplitude of a vibration and how does it affect the loudness of a sound?
The amplitude of a vibration is the distance the vibrating object (or molecules of air) moves from its starting point to its furthest position. A larger amplitude will make a louder sound.
5. Someone wants to play the first three notes of ‘Three Blind Mice’. (These will be in descending pitch.) Draw the bottles in the order in which they should be struck.
The bottles should be arranged so that the first has the least water in and the last has the most. (This gives a descending scale of notes.)
6. Describe two ways in which you could help children to understand that sound travels better in solids than in air.
Answers might include:
- placing an ear to a desk and making a quiet sound by scratching the desk;
- placing an ear to a large metal construction such as railings or a central heating system and making a quiet sound well away from the ear;
- using a string telephone;
- listening to a sound on the other side of a wall by placing a drinking glass to the wall.
7. Figure 14.6 is a child’s drawing of how a sound is heard through a door. List the child’s possible misconceptions (alternative frameworks) regarding sound. List the ideas that the child does correctly understand about sound
- The child is confusing cause and effect by suggesting that the sound makes the vibrations.
- The child may believe that sound will not travel through solids such as the door. The child knows, however, that the sound will be heard faintly and has explained this by suggesting that the sound travels through the gap under the door.
- The child appears to believe that sound travels by the movement of the air as though an air current is necessary.
- The child shows no sign of understanding that sound can be reflected.
- The child would need to be asked about whether the sound from the drum moves in all directions.
- It is not clear from the drawing that the child understands what a vibration is.