Activity idea: Jelly Baby Wave Machine

Jelly Baby Wave Machine

by Kate Bellingham

The jelly baby wave machine is not my idea – I found it on an excellent video with Alom Shaha.*  It is designed to be a demonstration for secondary school physics pupils, but I can thoroughly recommend this for an upper primary school demo, or a supervised make-and-do activity.

To make one 2m-long wave machine you will need:

• ·      40+ kebab sticks.  (I had to be strict about handing these out – lots of temptation to poke each other with them!)
• ·       At least 2.5m of duct tape (also known as gaffer tape or Duck Tape).  It is worth getting good stuff – chose tape that is very sticky and also flexible – parcel tape doesn’t really work.   
• ·      90-100 jelly babies.  Let’s be realistic, some will split and others will get eaten. 

When I ran this activity in my after-school STEM club for year 5 & 6, we made two of these, with about 6 children working on each one – though ours were shorter due to the available space.

I would recommend starting by showing the opening of Alom’s video, then getting the children involved in the planning:

• -       if the sticks are 5 cm apart and your wave machine is 2m long, how many sticks and jelly babies will you need?
• -       How can you keep the tape tight enough?  (I didn’t have clamps, and just stuck it to the table, but you might find a more effective method.  We started with chairs, and then found someone had to sit on them …..).  To make your machine reusable, you could put your tape around a wide drinking straw, put a stick through that straw, and then fasten the stick to the table instead. 
• -       How will you divide up the construction duties?  Alom mentions that the  exact distance between the sticks isn’t important, however, I found it is much clearer to see what is going on if they are fairly consistent.  Also, and perhaps more importantly, you will start to have problems if the sticks overhang more on one side than the other, or aren’t perpendicular to the tape.  You can make adjustments by pushing the jelly babies further onto the sticks to get the sticks to lie flat.  We found this was really important to make the machine work, and was quite time consuming (and the children started getting bored) so it is better to avoid this by getting the sticks on more accurately in the first place!
• -       What experiments do you want to try once it is built?  Do you want to take measurements?  What with?  Eg stopwatch / timer on phone and tape measure / metre rule. 

I found children enjoyed exploring it in different ways.  Some just loved watching the ripples, while for others there was a great deal of discovery involved.  “How can the wave go along when the sweets just go up and down?”   “What happens if you start a wave at both ends at the same time?”  And even if you don’t get the children involved in making the machine, they can still get a lot out of playing with it. 

Please let School Gate SET know how you get on, and any other advice for running this demo / activity with primary school children.

* I’ve just discovered that this idea should probably be credited to Jonathan Sanderson who created it for ‘The Big Bang’ Children’s ITV show over 10 years ago. I was presenter on that show for the first two series and worked with Jonathan, so I am delighted to give him this credit.  He also filmed the youtube video with Alom demonstrating the wave machine which has now been watched by tens of thousands all over the world.