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Railway Tracks

How the shape of wheels helps trains go round corners
Useful information
Kit List: 

- Large Board with tracks on it (two french curves placed on a table)
- The four sets of wheels (plastic cups and cans)

Packing Away: 

Lives in Misc. There'll be more cups in stores.



First get them to try and roll the flat wheels along the straight rails - it is just about possible if they are careful, but when they try on the curved track there is nothing keeping it on the rails...

Then maybe try the convex wheels, they should work a lot better. this is because when it goes slightly wrong to the right the left hand wheel effectively gets smaller, and the right hand bigger

So it will tend to turn left back into the track.

Then get them to try the blue convex wheels, these have the opposite effect if it goes wrong, the change in size of the wheels makee the problem worse...

This links in to equilibrium and we find that the convex wheels amplify any problems and the concave reduce. We can relate this to other equilibria and the standard marble on hills where it could be on the summit of a hill (unstable) and small perturbations cause it to fall into a valley. Valleys are stable to small perturbations. In a similar way while both wheels are in equilibria concave self corrects back and is stable whereas the other rolls but is very sensitive to small perturbations which cause it to diverge from the equilibria.

Talking about this and trains also leads on to Watt's Centrifugal Governer, this keeps trains travelling at a near constant speed by using feedback. The governor is connected to the engine out put and feeds back to the throttle. This corrects any external influence on speed, e.g. going down or up hill and reacts accordingly.

Risk Assessment
Date risk assesment last checked: 
Tue, 08/01/2013
Risk assesment checked by: 
Date risk assesment double checked: 
Sun, 20/01/2013
Risk assesment double-checked by: 
Richard H
Risk Assessment: 
DESCRIPTION The effects of various wheel edge profiles on cornering is investigated.
  • 1. Finger trap between the track and wheels
  • 2. Dropping one of the sets of wheels on a finger
  • 3. Finger trap between base and the ground
  • 4. Stray wheels may roll away causing a trip hazard
  • 1. Ensure tracks are clear before testing a set of wheels.
  • 2. Carry sets of wheels with both hands.
  • 3. Try not to leave or let kids lean on the floor by the tracks whilst wheels are being investigated.
  • 4. Catch wheels at the end of each round of testing; don't allow them to roll away unsupervised. Keep a track of each of the four sets of wheels, and if one is missing, locate it before continuing the experiment.

    Call first aider in case of injury.