Teaching Ideas for Sound and Waves
Here is a selection of ideas for teaching a sound waves topic to KS3 or the equivalent of 11-14 year olds. Sound and waves in general is a topic with great experimental potential. Simple activities can be used as starters to begin lessons and elicit students knowledge or as ways to demonstrate ideas. General trends such as rising pitch or volume can be shown easily. A microphone, oscilloscope or simple sound analysing software can be used to collect numerical data if needed.
The key ideas to demonstrate and emphasise are that sound is a vibration and that these vibrations need a medium to move through.
Simple Demonstrations and Activities
To show how sound travels differently through solids, liquids and gases – ask the students to work in pairs, one is to bang on the table top with their knuckles and the other to listen to the volume of the sound. The repeat with the second student listening with their ear firmly on the desk. Discuss their observations of the difference in volume. Discuss hearing sounds underwater in a pool or bath tub.
Tuning forks to demonstrate vibration – bang a tuning fork on a rubber bung and hold to the ear (to hear the sound) and then to your lip (to feel the vibration)
Large speaker connected to signal generator to show vibration – turn the speaker so the cone faces upwards, place small bits or paper or tiny polystyrene balls on top, play a note through the speaker and observe the vibrations. Ask students to predict what a higher or lower pitched note will do to the paper pieces. You can ask them to sketch what sound waves they think would represent each pitch and volume. This is a nice way of introducing amplitude and frequency as displayed in graphs.
Reeds out of plastic straws – follow the instructions here make and play reed instrument to produce a simple plastic straw reed. Need straws and scissors. Can shorten the straw by cutting pieces off to make a higher pitched note.
Rulers and change in pitch – twanging a ruler on the edge of a desk and quickly shortening the length hanging over the edge by pulling it in demonstrates nicely how more rapid vibrations produce a higher pitch.
Ripple tanks – all sorts of things can be shown with a ripple tank but at this level the demonstrations should reinforce the main topic, show how a more rapidly rotating motor on the dipper produces shorter, more tightly packed waves. Relate time and frequency, wavelength and distance to show wave velocity = distance/time = wavelength/time = wavelength x frequency. Students can measure the wavelength if a spotlight is shone down into of the tank and paper placed underneath. They can count the number of waves hitting the side in 30 seconds and find an approximate frequency.
The medium which is vibrating doesn’t move – ripple tanks can demonstrate this as the waves don’t push all the water out of the tank. It is important to compare and contrast the physical mechanism of tides and waves at sea as students are familiar with the tides bring water higher up the shore. This is of course due to an external force of gravity from the Moon and not a result of wave motion. This is a common source of misunderstanding in waves topics. Bobbing a cork up and down in the ripple tank shows this as the cork doesn’t move to the side. This principle can then be generalised to all waves including sound waves.
Standing waves in a tube – if you are feeling adventurous you can connect a clear, plastic tube (length >1m) to a microphone and cover the other end with plastic. Sprinkle some light particles (polystyrene balls, oatmeal, tissue paper etc) inside the tube and use a signal generator to produce a sound wave. Altering the frequency will cause the material inside to shift along to the nodes of the vibrations in the tube giving a rough measure of the wavelength.
Interpreting waveforms – supply students with a printout or display on the board various sound wave patterns and ask them if they can predict what sort of sounds they represent. Here is an example of the kinds of waveforms that can be used;
Why do double glazed windows deaden noise? You may have to explain how they are constructed (two panes with a vacuum between).
Why can no one hear you scream in space?
What will limit how high a note a human can sing? Why do women sing higher then men?
Why did people used to listen with their ear on railway tracks?
Is it hard to breathe near a loud speaker at a concert? Does thunder produce strong winds? What does this say about the motion of air as sound travels through it?