This is the CHaOS demonstrator website, mainly intended for our student volunteers. Click here if you were looking for our main front page.

Resonance

Introduction
What is the link between earthquakes and cello strings?
Useful information
Kit List: 

For earthquakes (large blue box):
- Earthquake table (wooden box with handle)
- Sections of tower for the above, made of perspex, magnets and springs.
- Dog on a swing.

Optional:
- Pan pipes
- Tuning fork
- Whirly woo

Packing Away: 

Pack into suitable boxes, as above.

Frequency of use: 
5
Explanation
Explanation: 

It's a collection of experiments illustrating resonance: the Earthquake Table lets you build towers and see what happens to them when vibrated near the resonant frequence, the Dog On A Swing gets across the basic idea of resoanance, the Giant Pan Pipes show how resonant air makes music, and the 'cello is a string driven by an oscillating electromagnet, which gets excited at resonance.

*** OVERVIEW ***

When you shake things too quickly or slowly, nothing much happens, but if you shake them at just the right rate - the rate they naturally shake at if you push them - the shaking builds up and builds up.

Possible activities:
- Trying to make the tower fall over by wobbling it at just the right rate.
- Comparing this to pushing a dog on a swing.
- Hitting or blowing across the pan pipes to make a noise.
- Hitting the tuning fork and talking about its resonant frequency
- Putting your ear to the pan pipes - they make a noise even when not hit or blown (not sure if this works with small pan pipes?)
- Whirling the whirly woo so that it makes a sound (check the whirly woo is working before demonstrating, if no sound can be heard there may be a hole that needs covering with tape)

Other things to talk about:
- Building design to withstand earthquakes.
- Seismic waves.
- How wind instuments work
- Resonance in cars, taps etc.

Tips for demonstrating:
- Everyone enjoys turning the handle on the earthquake table. Try to make people, even little children, take turns.
- The experiment links well with Seeing Sound, and can share equipment and demonstrators.

*** BASIC PROCEDURE AND EXPLANATION ***

- Start by getting someone to turn the handle of the earthquake table slowly. A tower three blocks high works best. It shouldn't shake very far. Then ask what they think it will do if they shake it much faster. Will it wobble more?

- It doesn't (or, at least, not much). Now get them to try an intermediate speed. It should be possible to get the tower shaking a long way at just the right speed. You may need to practise doing this to show unconvinced children with poor handle control.

- Try to explain why this happens. The swing is useful here: to make someone swing higher, you push them once every time they come past, so that they build up a little bit more each time. Get the kids to do this to the dog. Also show them that pushing at the wrong rate means that you're sometimes speeding him up and sometimes slowing him down, which is why it doesn't work properly. Then show them that it also works when you wobble the base of the swing: just the right rate makes the dog swing high.

- The kids may then be able to explain why the tower swings most at a particular frequency, and you might want to talk about designing buildings to withstand earthquakes.

- The pan pipes make a sound if you blow across (not into) the ends, or hit them with bats or bits of card. Explain that this is the air inside shaking, and link in with the Seeing Sound experiment if it's about. It's possible to use the slinky spring to get across the idea of a standing wave.

- The pan pipes also make a sound when you put your ear next to the end and listen. This is becasue any sound in the room at the right frequency is magnified by the resonant pipes.

-The whirly woo only makes a sound when you rotate it at the right frequency. Similar ideas to the above but 100x more exciting for kids than a panpipe.

- Hit the tuning fork and explain that the note that you hear corresponds to the resonant frequency of the tuning fork. Again, draw a parallel to the swing and that the note you hear is the frequency at which the tuning fork 'likes' to vibrate. With older kids you can talk about how initially the fork is vibrating at lots of frequencies but all the ones which aren't the resonant one decay quickly, like how the swing's amplitude quickly decays if you push it at the wrong frequency.

*** OTHER THINGS TO TALK ABOUT ***

- All sorts of things can resonate, and we'd often rather they didn't. Many people will have heard about the millenium footbridge in London, which wobbled as people found themselves walking in step with the wobbling. It had to be closed, and was fixed by fitting damping, which is also the way a car's suspension tries to avoid resonating. Going further back, the Tacoma Narrows bridge failed catastrophically due to resonance with the wind.

*** SCIENCE BACKGROUND FOR DEMONSTRATORS ***

Anything that you know about resonance will come in useful for this experiment. Most things can be modelled as damped, driven harmonic oscillators, yielding a second-order differential equation with a sinusoidal right-hand side and a familiar set of solutions. Trying to go into mathematical detail with little children is a mistake, though. Even the words `resonant frequency' can be off-putting.

You may like to note (so to speak) that the pan pipes are tuned to a pentatonic scale.

Risk Assessment
Date risk assesment last checked: 
Mon, 16/12/2019
Risk assesment checked by: 
lucyhart.042
Date risk assesment double checked: 
Thu, 16/01/2020
Risk assesment double-checked by: 
jpichon
Risk Assessment: 

Using various models to explain the concept of resonance. There's a box, which shakes a model tower (held together by magnets) when a handle is turned. There's a model swing with a dog, a set of panpipes, a tuning fork and a whirly woo.

Hazard Risk Affected Person(s) Likelihood Severity Overall Mitigation Likelihood Severity Overall
Box on table Falling box or tower blocks could hit children on the head, hands or foot. Public 4 4 16 Tape the box to a table, and not so high that falling tower blocks could hit children on the head.
Call first aider in case of injury.
2 3 6
Finger trap Finger trap between the handle of the box and the table on which it's mounted, or between magnets. All 3 3 9 Mount the box with the handle far enough clear of the table that there's no possibility of a finger trap.
Be careful when setting up/packing away.
Call a first aider in the event of an emergency.
1 3 3
Whirly woo Child or demonstrator hitting someone with the whiry woo while swinging it. All 3 3 9 Make sure there is a clear space in which the whirly woo can be used.
If the children seem too excited, demonstrate the whirly woo yourself.
Swing the whirly woo above your head so that it is above the height of the children watching and so can't hit them.
Call first aider in case of injury.
2 3 6
This experiment contains mains electrical parts, see separate risk assessment.
0
Images
Publicity photo: 
Experiment photos: