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Mould Effect (Self-Siphoning Beads)

Fri, 26/01/2018 - 12:24 — Sarah
Introduction
Public summary: 

Why on earth do the beads have to go up to come down?! Watch them fly out of a beaker, looping and corkscrewing, and find out about the amazing Mould Effect!

Letting a chain pull itself out of a beaker under its own gravity
Useful information
Kit List: 

25m chain of metal beads (in 5m sections)
A shorter length of chain
Lidded pot/beaker to store them in and siphon them out of
Something to wrap the chain round (e.g a reel) in order to stop it getting tangled in storage.

Packing Away: 

Carefully wind the chain round the reel so it doesn't get tangled.
The shorter chain and small beaker lives in the small grey floating box.
The larger chain and reel lives in the misc box.

Explanation
Explanation: 

https://www.wired.com/2013/07/the-physics-of-that-gravity-defying-chain-...

https://www.youtube.com/watch?v=_dQJBBklpQQ

https://www.youtube.com/watch?v=-eEi7fO0_O0

https://www.youtube.com/watch?v=6ukMId5fIi0

This is a provisional explanation - I plan to write this up properly later - Jared

Method:

Place the chain inside the beaker, hold the beaker in your hand then throw one end over the side so that the end outside the beaker is longer than the section going between the top of the beaker and the coiled up chain (so that gravity is able to pull the rest of the chain out of the beaker). For the small plastic beaker currently in the box, 15m works best.

Let go and watch as the rest of the chain flies out of the beaker, producing a surprisingly wide arc into the air as it goes. If you're lucky you may see coils and loops, appearing to be frozen in space even as the chain continues to move.

Explanation:

The weight of the chain outside the beaker is greater than that of the free section inside the beaker, so the chain is pulled out, at some speed. However, due to Newton's 1st and 2nd laws, the individual beads of the chain can't change direction instantaneously. Instead, it takes a continuous force pulling them round in a circle until they are travelling downwards towards the floor - hence the arc.

If the chain hits the side of the beaker as it's doing this, the disturbance will attempt to travel away from the point of contact - i.e. back towards the bottom of the beaker. However, the chain is moving fast enough to counteract this, and so the net effect is that this disturbance barely moves. This is the reason for the standing coils and loops you might observe (it may be that the wave velocity equals the speed of the chain at this point, but I'd have to check this).

Further Points:
You could try drawing an analogy with siphoning a liquid using a long hose/straw.

Floating
This experiment can work well for floating however, you'll want to use the short chain and be careful not to fiddle while carrying it else you'll tie it in knots. 2 goes is probably sufficient for a 5 minuite demo and ask them to think about the forces, gravity and acceleration before trying it. Bring in momentum for advanced groups and talk about needing all the beads to move at the same speed and how they can't change direction instantly. Analogy with running round a corner and needing a wide bend to keep the same speed (400m running track).

Risk Assessment
Date risk assesment last checked: 
Fri, 26/01/2018
Risk assesment checked by: 
Sarah
Date risk assesment double checked: 
Sat, 03/02/2018
Risk assesment double-checked by: 
jaredjeya
Risk Assessment: 
DESCRIPTION Letting a beads pull itself out of a beaker under its own gravity
RISKS
  1. The beaker may fall and hit the ground if placed on the edge of a table, presenting a broken glass risk
  2. The beads may hit someone or present a strangulation risk
  3. Trip hazard due to beads on floor
  4. Choking hazard
  5. Nickel allergies
  6. Demonstrator falls from chair/high place
CONTROL MEASURES
  1. Hold the beaker in your hand instead. If the beaker does fall and break, immediately clear away the broken glass with a dustpan and brush and dispose of the pieces appropriately
  2. Ask audience to step back (at least 1m) to avoid being hit and hold the beaker away from your body. Do NOT carry out in a crowded space. Make sure audience is paying attention. Pick up the beads yourself after it finishes, do not let children play with it.
  3. Tidy up the beads as soon as the demonstration finishes. Ask viewers to step back until you're done. Potentially siphon beads into a large tray.
  4. Do not let anyone play with the beads or place them in their mouth.
  5. Check with audience that none are allergic to nickel.
  6. If standing on a chair or at the top of steps then ensure firm footing and descend before explaining. Only do one elevated demonstration per group to avoid getting on/off the chair whilst distracted by explaining.
IN CASE OF ACCIDENT
  1. Tidy up glass, seek a first aider
  2. Seek a first aider
  3. Seek a first aider
  4. If a long length has been swallowed, do NOT attempt to pull it back out, but cut off the free end. Call a first aider.
  5. Seek a first aider
  6. Seek a first aider
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