- Recognising that the sound needs a medium to travel
- Understanding that sound travels through different mediums, including solids, liquids, and gases.
|Sound source, bell jar, vacuum, a string telephone, balloon with water, water, different medium for example wood, metal, glass, plastic, ceramic etc.
Hand out Classroom Material: How sounds travel (Part I), let students read and answer questions. Then show them the following demonstrations:
- Place five coins, in a line next to each other, flat on the table. Flick a sixth coin so that it hits the first coin in the line. Last coin in the line will move.
- Place an alarm clock or an electric bell in a large bottle. Let the bell ring in air. Then pomp the air out of the bottle and let the bell ring in a vacuum.
- Place a candle in front of a speaker. Turn on the speaker (frequency 5 – 10 Hz). The flame flickers indicating air movement. (Instead of the demonstration the included video can be displayed).
- Use a coiled spring (slinky); send pushes and pulls along the spring.
Discuss with students their observations and help them to construct the following ideas:
- Energy can be transmitted through the particle of a substance.
- Sound needs a medium to travel through; it cannot be transmitted in the absence of particles.
- Sounds waves are alternate compressions and expansions caused by the back-forth motion of the particles of a medium.
Divide the class into groups and hand out Classroom Material: How sounds travel (Part II). Give each group a sound source and materials to investigate. These can be two cans (or paper cups) connected with a string, a balloon with water, book, and different medium like wood, metal, glass, plastic, ceramic, etc. In this activity students are asked to design their own investigation to find out if sound can travel through different materials and through which material(s) sound travels the best. Walk around and give students some tips if necessary. Ask them about the designs of their (fair) investigations.
Finally let each group present their conclusions, allow students to debate their reasoning.
- How sound energy is transmitted?
- Why can you not hear the bell ringing in the jar?
- Can you hear the sound from a sound source when it is held in the air?
- What medium was the sound travelling through in this case?
- Does sound travel through string?
- Can you hear your partner better when the string is wet or dry?
- Does sound travel through glass? Wood? Etc?
- Do sounds get weaker with distance?