Resources: The handout, craft materials, scissors and tape.
From KS2, the students should be aware that sound is a form of energy that travels in waves through a medium, such as air, water or solids. They should also know that vibrations are the source of sound.
Ask the students: why can no one hear you scream in space?
With the students, work through the presentation, answering questions as you go. Emphasise that sound needs a medium to travel and explain how sound travels. Then, ask the students to complete the investigation to design and build a passive speaker, using the worksheet for guidance.
Careers Film: Crossrail Engineers: Juliet Murray, Track Field Engineer
Expert Film: Watch the Expert Film with Jon as he explains how sound travels through different mediums through the use of a tuning fork.
The students will build a passive speaker. Passive speakers do not require a power source; instead, they channel sound waves into the same spot to create the effect of increasing volume.
The students' designs should include a slot to put a mobile telephone in and an opening to allow the sound out. The rest of the design is entirely up to them.
Support: Discuss possible designs as a class. Technicians might be able to create some designs that students can observe and base their own designs on. These can also be used to evaluate so the students know how to evaluate before they critique their own. There is also a question on the handout.
Challenge: The students can observe different designs in the class and then design a second version of a passive speaker, taking into account their own evaluation and the work of others.
Ask the students to review their findings from the practical and then complete the questions on the end of lesson assessment quiz.
When we think of sound, we must think about waves and vibrations. Sound is basically a vibration that travels through matter. Matter can be anything from a gas, to a liquid and a solid. To reach our ears, the sound waves must travel through the medium first. When movement takes place, a vibration is initiated. For example, if someone knocks on the door, a vibration is created. This initial vibration will then cause further molecules to vibrate, and so on. It is the spreading of the vibration through the molecules that permits the sound to travel. The vibrations will cause the molecules to move backwards and forwards until the sound wave is created. The wave will have the same frequency as the object that made it. Sound waves are longitudinal waves that cannot travel through a vacuum, only through a medium. They can be diffracted, reflected and refracted.
The sound must travel through whichever medium to propagate because it relies on the vibrations of molecules to move. These sound waves will travel at different speeds through different mediums. For example, through the air, the waves will travel at around 343 metres per second. This is different in water. Sound waves travel a lot quicker in water than they do in air. In fact, they travel four times faster in water than they do air. Sound travels even faster through solids such as steel. It is reported that sound waves travel at a whopping 4,512 metres per second through steel. As you can see, the speed of the wave is very much dependent on the density of the medium it is travelling through. Steel is a lot denser than air, which means that sound travels a lot quicker through the solid.
As humans, we must hear the sound to process it. When sound waves hit the external ear, it passes through the auditory canal, which then causes the vibration in the eardrum. This vibration will cause the bones in the middle ear to move, which permits the vibrations to further propagate to the fluid in the cochlea. This vibration is responsible for the movement and stimulation of the hair cells within the inner ear. These vibrations are later turned into electrical messages which permits the brain to interpret them as sound.