Teaching Waves and Sound – Ideas

An overview of waves and sound with some ideas of how you might teach them. Please add ideas to the comments or through twitter @natkin.

feynman

If we follow the philosophy of Feynman it is not about transferring knowledge without a context. If we use this approach we can go beyond simply being able to answer exam questions into the realms of learning.

I find intuition a good starting point and have written a blog post on it here

Starting with waves

Get the students to wave to you and they all can.  So they understand the concepts of waves. Have a discussion of what makes a wave, a wave.

Concept that it is a repeated oscillation about a point in language appropriate to your students

How might we describe a wave?

The students sit back to back . One can see the video of the queen waving and has to describe to the one who cannot see who has to try and match what is on the screen. I stand behind them telling them when they have got it right

If you try describing how the Queen waves in a way that everyone else can understand . Its a pain saying  “She waves her hand backwards and forwards repeatedly and quickly at the same rate without making it go very far from the central position”

Then introduce the terms

Frequency – Number of times something happens in a given time. What is the frequency of your lessons? 5 per day. Frequency of buses ? 2 per hour. Frequency of waves? Number of complete waves /cycles per second.

Amplitude – Students often confuse this with height and they need to ensure it means the maximum displacement from the rest position

Now we can say of the Queen  “She has a high frequency, but low amplitude wave”  (it seems to have changed over the years , most people remember it as slower with a higher amplitude )

Next was a demo of a slinky how might we transfer energy down the slinky? 2 ways side to side/up down or in and out

Ways of transferring energy using a slinky

Relate these to terms transverse and longitudinal waves and how there is no mass transfer of molecules, simply energy transfer. A bit of masking tape demonstrates this well.

Revise the ideas of high low frequency and amplitude with the slinky.

This may be a good time to explore the relationship between frequency and energy . This is fairly intuitive – If you walk into the sea and waves hit you more frequently then you will clearly notice that higher frequencies transfer more energy. Relating this to the electromagnetic spectrum waves of frequency greater than that of visible light – Ultra violet and higher can be dangerous.

We can also see wavelength clearly demonstrated on a slinky

You can see nice standing waves using an electric toothbrush and elastic outlined here

You can also demonstrate  wavelength and it’s relationship to velocity using a hand wave. Give them a pen to hold over a sheet of paper. Pull the paper with an increasing speed and you will see an increasing wavelength being drawn on the paper (see below) You can also relate this to the wave equation

Velocity (m/s) = Frequency (Hertz) x Wavelength (m)

The frequency is constant and the wavelength increases as the velocity increases

Excerpt from a lesson

Having had the terms described using Pose/Pause /Pounce / Bounce to gather their ideas they were then given 2 minutes to perform waves of high/low frequency, large/small amplitude and long/short wavelengths. Some interesting ideas were demonstrated with students also whistling high and low frequencies. I know I am teaching well when my students surprise me.

Jelly Baby Wave machine

Then they were given a length of duct tape, barbeque skewers and jelly babies to make the jelly baby wave machine. seen here

This is an ideal experiment to get the students to build the problem. What might happen if …?

Ideas:

The distance between the sticks was changed

The tension was changed

The jelly babies were moved closer to the centre

Half of each jelly baby was eaten

Sound

Following the concept of waves leads us into sound a longitudinal wave. Show with a slinky

Other possible demos

Frequency and Sound

Hum the National Anthem with your hand on your throat. Hum in louder (higher amplitude) , higher frequency etc. What do you notice?

Vibrations of your vocal cords. What would happen if you have no vocal cords after say a larnygectomy

How can you make a metal rod sing?

Hearing Tests

If there is only one thing to tell students it is that every loud sound damages your hearing. In quiet societies old peoples hearing is far better than it is in noisy societies .

An online hearing test is here

http://www.actiononhearingloss.org.uk/your-hearing/look-after-your-hearing/check-your-hearing/take-the-check.aspx

The worlds quietist room where you can hear your organs !

Following this you can go into the realms of making music and the straw oboes

http://www.physics.org/interact/physics-to-go/straw-oboes/

Ask the question what would happen if…?

The straw became very short? – Would go into ultrasound

The straw became very long? – Would go into infrasound – which may attract elephants

Can you shatter a glass with just your voice?

This can lead you into resonance and the must use footage of the Tacoma Narrows Bridge

and this truly spectacular demonstration

Taken from here

Or make a very annoying sound from a piece of paper that will make the other teachers hate you

Speed of Sound 

You can use Audacity – free and brilliant software to measure the speed of sound

National STEM Centre resource here or

Or by echoes

Speed of sound with echoes

Apps for Sound

String for iPad – Simple app that lets you play with waves on a string here

Higher level em spectrum stuff  from Loughborough here

Fourier Touch – Great for showing beat frequencies and playing with sound waves here

Review of these 3 here

There are a few oscilloscope apps around. I use oscope here

Lots of sound level apps that are great to leave on to keep class noise levels at a reasonable level.  Decibel 10 gives you peak values etc here

Not sound as such but the seismometer app is useful here

Uses of Sound

10 wonderful uses here

Really interesting list here might need some verification

Making instant coffee in mid air – Acoustic Levitation here

As a weapon – Anti piracy or demonstration devices LRAD (Long range acoustic devices) – report here

Feel free to add ideas to this through comments etc – I’m constantly updating it

9 thoughts on “Teaching Waves and Sound – Ideas

  1. Great ideas Neil and i’ve shared them with the student-teachers i work with. One of my favourite activities with sound, which I suspect would follow the activities you describe, is thinking about wave properties of sound: diffraction through doors, reflection (echos) but in particular I like using a pair of speakers from an oscillator on a set frequency, then getting pupils to move around the room and see if there are any areas where it is louder (constructive interference) or quieter (deconstructive). A particularity good A-level class a few years back manage to work out the frequency from the distance between the maxima. It’s success depends on the room acoustics but it’s always fun watching them move around like zombies anyway!

    1. Nice one Mark – Will add this when I do an update! I go outside the room and get them to tell me why they can hear me but not see me as well.

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