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Lockdown Challenge: Going out with a bang

Image credit: Pedro Joel Landrau/Dreamstime

We conclude our series of family-friendly Lockdown Challenges with an opportunity to ride the radio waves… and make very loud noises!

We’ve had a lot of fun with the Lockdown Challenge for the past few months. Largely blessed with good weather the majority of these challenges will have been accessible to most, and if the schedule was a bit heavy for some there is now a back catalogue of ideas to inspire your family in the future. The majority of these ideas (all still available on this website), although designed for engineers at home with their restless offspring during the lockdown, are equally appropriate for projects at schools, youth clubs or any environment where engineers can lend their expertise and enthusiasm to introduce inquisitive children (and they are all inquisitive) to the joys and possibilities of engineering.

Appropriately, we are going to go ‘over and out’ with a ‘big bang’. First up this week, Crispin Andrews shows how you could encourage a budding radio engineer to set up their own radio station. Following that, we have Neil Downie’s final experiment and, true to form, he is finishing with a Big Bang. 

The IET has a host of resources, which adults can use to engage children with the world of STEM.

Lockdown Challenge #31 – How to make your own radio station

Does someone in your family fancy themselves as a bit of a DJ? Maybe they just want to play their favourite tunes to their mates, or spend hours chatting away about football, celebrities, or UFOs?

Whatever your chosen subject, if you want to start your own internet radio station you only need a PC or tablet with a microphone, an audio cable, which you plug into the microphone jack and the headphone jack, and access to skype or a web-based streaming service.

Listeners tune in on their computer, smartphone or tablet, not with their usual radio set. It is possible to use a smartphone, but there are fewer apps available.

How to set it up

  • Get some apps: one to play music files, one to turn the audio feed into a streamable source (e.g. winamp SHOUTcast), one to act as a server to share the seam to listeners (e.g. Icecast, Andromeda, Peercast, Quicktime broadcaster).
  • Decide on your streaming service – some are free, others you pay for such as Live 365, radiojar.com and radio.co. Work out what you want to do on your station and pick the option that best suits that content.
  • The stream server doesn’t have to live on the same computer as the audio source, which is good as streaming requires a lot of bandwidth to accommodate multiple listeners. Use your PC to play the music or the talking and then stream over the internet to a dedicated radio stream server equipped with high bandwidth. You’ll have to pay for it, but not that much (try https://myradiostream.com/ for example).
  • Create a cool name for yourself, one that is short and easy to pronounce.
  • If you’re talking, add acoustic panels to the walls to improve the sound quality or add soundproof foam to furniture.
  • If you want to use copyrighted music, you’ll have to pay for it. Not so if you’re just playing your own. There’s royalty-free music out there on YouTube, Audio Blocks and other places, but you’ll still need a music licence to play it.
  • In the UK, PRS (the Performing Rights Society) collects royalties on behalf of artists, composers and cover music that’s played on TV, radio, and online.
  • Also in the UK, the PPL represents the interests of record labels and collects royalties from radio stations on their behalf.
  • A royalty-free licence is usually cheaper than a statutory one as you’re purchasing the rights to use the tracks forever, not buying tracks for a set amount of time.
  • If you want to report on the news, subscribe to newsfeeds; Google Alerts and Tweetdeck, for example, can help you locate news stories of interest.
  • If you want to stay anonymous, you can put up an image for people to see as you play your music or say your piece.
  • Plan shows in advance so listeners know what they can listen to and when.
  • Put the word out there on social media to get more friends to sign up, ask friends to recommend you and spread the word.
  • If you get enough followers, you might even start making some money through advertising.

Lockdown Challenge #32 – The Biggest Bang since The Big Bang

My Christmas-party expert friend Ebenezer says" “Bangs from Balloons? Bah, Humbug! Balloons don’t go bang, they go pop.” Not so. With a little effort, you can prove Scrooge wrong and make a really Big Balloon Bang. And what about an even bigger bang with the Boyle’s Law Banger, which you can make out of an old bike pump? But first, more bang from balloons... 

Do you have ear-defenders? If you don’t, do all your Big Bangs outside. Now find some balloons; the stronger and bigger the better. Take a balloon and inflate it until it’s full and somewhat pear-shaped. Now pop it with a pin. Nice pop? A little bang, maybe? You can do better. Much, much better.

Now take another balloon and simply inflate it. Use a pump, a balloon pump, or, even better, put the balloon on a small piece of plastic tube, use duct tape to keep it from coming off and use a bike track pump or foot pump. A valve from an old inner tube can make the connection to the plastic tube. Keep on inflating the balloon... and inflating it...  and inflating it... until... BANG! It’s gone. With luck, that was much, MUCH louder.

Try testing bang loudness with a phone sound app; make the measurements fair by exploding at the same distance. And take a look at the exploded balloon pieces. The pic shows a pin-exploded balloon and a pressure exploded balloon – and the YouTubes give insight into why the shapes are different. 

Here is a pin popping a balloon:

Here is a balloon popped by pressure by Dr Yan Wong, from a BBC programme rather appropriately called 'Bang Goes the Theory':

What next? Bigger balloon? Even better, try putting one balloon inside another similar one. Inflate the double-balloon, now the pin... with luck, that will be a nice big bang. Try exploding a double-balloon by pure pressure. Prepare for a serious bang.

Boyle’s Law says that when you squeeze air down in volume X times then the pressure will go up X times. Squeeze the gas to a tenth, and it will go to ten times the pressure and... BANG!

The picture below shows the stages in making a Boyle’s Law Banger, from a bike pump at the bottom to Banger at the top. You’ll need an old ‘frame’ bike pump, a soda bottle, glue, and 40-50mm-wide ‘Sellotape’ type tape – the thinnest grade. First saw off the tyre-filling end; make sure that the piston goes nearly to the end of the tube.

Now saw the end off a 1 litre soda bottle, 30mm of the bottle neck past the screw thread part, a total of ~50mm. Sandpaper the pump end if it is shiny/slippery and maybe coat with cyano glue. Similarly the inside of the soda bottleneck. Glue this onto the end of the bike pump with hot-melt glue. Make a really good job of it and, for extra insurance, wrap a couple of turns of duct-tape around the joint.

Make as large hole as you can in the bottle cap. Now ‘arm’ your Boyle’s Law Banger by putting sticky tape over the end, then screw the cap firmly on over it.

With ear-defenders on, prepare to pump the bike pump just once, but pushing very hard. With luck, the volume will go down, the pressure will go up and... BANG!  

If you find it hard to get to the necessary force, try putting something soft and grippy like Blutack on the pump handle, place the handle on the ground and hold the barrel and push it vertically down onto the handle.

The energy in compressed air is a bit more than atmospheric pressure × volume of air in the pump. That will typically work out at 10 Joules. The crack crosses the tape at the speed of sound in plastic, maybe 2,000ms-1. With a 20mm crack, that gives 10 microseconds crack time. Power is energy/time = 10J / 10-5s = 106W; so your Boyle’s Law Banger emits a megawatt of power.

Challenges

Can you make a triple balloon and explode it?

Does a balloon make differently shaped pieces when pierced at the top rather than the side?

Can you get a video of the Boyle’s Banger exploding in slow motion? Some phones record slo-mo.

And finally, what about an underwater bang? It won’t sound as loud, but it is powerful; look at what it did to the washing up bowl below.

If you liked this, you will find lots more fun science stuff in my books like 'The Ultimate Book of Saturday Science' from Princeton University, and for lots of other things (and a free copy of the 'Exploding Disk Cannons' book), visit www.saturdayscience.org

Many thanks to Crispin Andrews and Neil Downie for their contributions to this column.

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