The tuning fork produces/stops producing a sound when clicked.
In ‘Low Detail’ mode, clicking the tuning fork causes it to vibrate and sends a sound wave out in all directions. These waves move as a series of regions where the surrounding air particles are compressed together (represented in the diagram by bold white lines) and move apart (represented by the paler white lines).
In ‘High Detail’ mode you can look at this motion more closely. Ensure the children appreciate that air molecules are incredibly tiny – too small to see even with a microscope.
As the wave passes through the air, have the children focus on the movement of an individual particle. Click on ‘Single’ to see this in close-up.
Common misconception: It is worth pointing out to the children that although these are waves, they are not like water waves! The waves move backwards and forwards in the direction of the movement of the energy. This can be effectively demonstrated with a ‘slinky spring’ if you have one:
Holding one end of the slinky, stretch the spring across the floor and have someone hold the opposite end. Now push and pull the slinky at one end in the direction of the spring itself to create a compression, and watch as a wave travels along the spring. You can continue to create these compression waves by repeatedly pushing the spring from one end. This movement represents the vibration of an object creating a sound. The spring represents the air (or other medium) that carries the sound away from the source. The children should see that, just as in the on-screen simulation, each coil simply moves to and fro about a fixed point – the energy moves out from the source along the spring as a wave, but each individual coil moves only a short distance.
Ideas for Demonstration/Activities:
Model the passing of sound energy from one pupil to the next by having a number of them (say 5 or 6 initially) stand in a line with arms outstretched and placed on the shoulders of their neighbour. Each pupil will represent a particle in the air.
The person at the start of the line (teacher) ‘vibrates’ with a gentle push to the shoulders of the pupil next in line and then return to the initial position. Once pushed, the next person does the same and so on down the line to create a wave (ensure children know that each particle can only move to and fro so they push gently and return to their original position!).
The children observing the demonstration should be able to see the wave of sound move along the line.
The explanation could be extended to include the fact that the vibration will eventually reach an eardrum, causing that to vibrate so that the sound may be heard.
To extend this model further to represent sound passing through liquids and gases (perhaps when looking at the ‘What’s the Speed of Sound’ tab), increase separation between the children and have the children simply tap a shoulder to represent the vibration (they may need to take a few steps before returning to their initial position) – passing the vibration should take longer as separation increases, showing that sounds travel more slowly in liquids than solids and even more slowly through gases.
Place hand on throat and feel the vibrations as a sound is made!
Encourage the children to focus on the fact that the tuning forks are vibrating at different rates. If the vibration is quicker, the compressions are more frequent and a note of higher pitch is produced.
If possible, relate this to musical instruments with which the children will be familiar, such as a guitar, recorder or flute, etc. They will (hopefully) be aware that different notes are produced in various ways (e.g. by changing the length of the string of a guitar or pressing keys/covering holes) – explain that these actions alter the frequency of the vibrations (how many sound waves are produced each second).
Ideas for Demonstration/Activities:
Hold a ruler firmly over the edge of a desk and ‘twang’ with different lengths of ruler protruding – this is a really simple way of hearing the variation in pitch with length of ruler. Then you can do this with elastic bands stretched by different amounts, but the rulers tend to show more definite pitch changes – this is an easy, simple investigation for the children to do themselves.
Shrieking balloon – place a hexagonal nut inside a balloon, inflate and tie off (if children do this themselves, encourage the use of a balloon pump to prevent accidental swallowing of the nut). Holding the balloon firmly at the tied end, spin the balloon at different speeds. The nut generates vibrations in the skin of the balloon and produces sounds of different pitch, dependent on the speed of rotation. (If you use a smooth penny instead of a hexagonal nut there are no vibrations, no sound!)
Common Misconception: Children often confuse volume and pitch. Try to encourage the use of the terms high and low when referring to frequency. Loud and soft/quiet are terms relating to volume, which is a measure of the amount of energy of a sound, or the size of the vibration. You can show this with a drum and some beads/rice/similar placed on the skin. If you tap the drum lightly, the vibrations are passed to the beads, which move up and down. Hitting the drum harder produces a much louder sound – the vibrations of the beads are much bigger as they have more energy, but the sound produced does not change in frequency (the drum only makes sounds of one frequency).
Ask the children for ideas about evidence that sounds can travel through a variety of materials, not just through the air.
Try putting an ear to the desk and tapping lightly with fingertips/fingernails elsewhere on the desk top – the sound travels very well through the desk!
The scenes depict different materials through which a sound might travel – click on the ‘Air’ scene to find information about the speed of sound. Ensure the children understand that this is how quickly the sound can travel away from its source. So, for air this is 350 metres per second i.e. if the girl and boy in the picture were 350m apart, the boy would hear sounds from the girl 1 second after she made them. If he were 700m away, it would take 2 seconds for her sounds to reach him, etc.
Have the children predict how the speed of sound might change in the other scenes before revealing the actual speeds and explanations.
Common Misconception: It is important to notice that ‘Speed of Sound’ is different to frequency. Whilst the frequency measures how quickly the sound waves are produced, it does not have an effect on how quickly the sound itself moves through a medium. The speed of sound is determined by the conditions through which the sound travels. High and low frequency sounds travel at exactly the same speed under the same conditions. Think of ‘speed of sound’ relating to how quickly any sound produced in one place will travel to another before it can actually be heard/detected.