Science put to the test
And so, to quote Sinatra, the end is near. It's the final post for the Big Contraption blog. If you missed the live broadcast (where were you?), watch it in all it's glory:
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I realise it's taken a long time to post this final entry, but i'm hoping you'll find it worth the wait. So, I hear you ask, what science was put to the test in the Big Contraption?
The bike Liz was riding might have looked a little odd: but it's a model that has twice broken the world speed record for a conventional upright bike. The bike was attached to the shaft of an old DC motor. Instead of using electricity to make the motor turn, we turned the motor to generate electricity, via Faraday's principle of electromagnetic induction. So the faster Liz pedalled, the more electricity she generated. An inverter converted the generated direct current (DC) to alternating current (AC), and was set up so that an input of 12 volts DC, would produce 240 volts AC (the same as used in your home wiring).
The motor which turned the belt on the Van Der Graaff generator was designed to operate at the voltage produced by the inverter. Once Liz was pedalling fast enough to generate 12 volts DC, Jem stepped forward to 'collect' the electrical charge from the dome of the Van der Graaff (around a quarter of a million volts, but a tiny current).
Because his feet were insulated from the ground, Jem could use his body as a conductor. When his finger approached the grounded metal of the unlit Bunsen burner, there was enough voltage to ionise the air and create a large spark (the gas supply had been pre-activated by a special effects expert). Doing this with high voltages (even at low currents) creates burn points on your fingers and can potentially interfere with your heart: so don't try this at home. It's dangerous.
Once lit, Jem adjusted the Bunsen burner, allowing air in to make the flame burn more fiercely so it would quickly burn through the rope above. When the rope broke it activated a lever attached to a compressed tank of gas (carbon dioxide, like some fire extinguishers). This fed into an air amplifier which used aerodynamic principles to convert a relatively small amount of high pressure air into a large amount of low pressure air causing the bunny to dramatically inflate at high speed. The bunny ears were due to be the last part that inflated, breaking a laser beam that was positioned at the top of the structure. As we all know, in the live broadcast the bunny didn't fully inflate, didn't break the beam, thus requiring a special effects expert (aka 'The Man With the Stick') to step in.
The laser beam detector switched off an electrical circuit connected to a solenoid, which was holding a bowling ball in place. When the beam was broken, so too was the circuit realeasing the bowling ball down a specially made chute. It gathered momentum as it travelled downhill, hitting a second ball. It passed its momentum to this second ball which was enough to propel it uphill and onto the next part of the contraption.
The second of the bowling balls hit the lever on a valve that released pressurised water from a pre-rigged hosepipe into a Perspex tube. The ballcock floating on top of the water was pushed up the tube until it hit a button at the top (The water flow carried on for a short time, spurting out of the top of the tube).
The button activated a lever that started a pre-programmed sequence of notes, stored on an electronic device and broadcast through a speaker attached to the end of a pre-lit Rubens tube.
A Rubens tube (also known as a standing wave flame tube) uses flames to display sound waves visually. Sound is simply waves of air pressure, so when the speaker produced noise, it created standing waves of higher and lower pressure points in the propane gas inside the tube. There were equally spaced holes along the tube: more gas escaped through holes where pressure was higher, and less where it was lower, creating a pattern in the flames that changed depending on the pitch and volume of the noise.
The flames needed to be in the right place and high enough to heat the digital thermometer to 50 degrees. When this was reached, it triggered a switch which broke the circuit supplying current to a pair of electromagnets. The electromagnets were holding Dallas' chair at the top of a slope. When the current stopped, they stopped being magnetic, and released Dallas down his track at a walking pace.
There was a pair of very strong ferromagnets attached to the back of his chair and a corresponding pair on Dr Yan's cage. These permanent magnets were glued in such a way that, as Dallas got closer to Dr Yan, the like poles approached each other. This invisible force between them propelled Dr Yan across a 2.5 void - that you at home voted for - without any physical contact.
When Dr Yan reached the other side of the void his cage knocked a beaker tipping a ball bearing out of a tube which travelled down a specially made ramp. It slid down a thin tube and hit the enter button on a computer keyboard that triggered the programme to send the robotic arm into action.
At the end of a pre-programmed sequence of flexing actions the robotic arm hit a big red button that lit the fuse on a small rocket stuck into a polystyrene sphere. This was fired down a zip wire, and travelled at high speed from inside the hangar to outside, where the Bang Goes the Theory logo was rigged up. As the rocket impacted on the logo, it exploded with a very impressive bang.
And so that's it for the Big Contraption blog. Steve, the Community Producer, and I hope you've enjoyed it and feel inspired to put science to the test for yourself.
© 2012~RS~q~RS~~RS~z~RS~33~RS~)