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How does a 'Slinky' toy work? Explaining to a 4 year old...

If you're a parent I'm sure you're well aware that young children can ask the 'Why' question up to 300 times a day... ?


So I'm spending some time with my 4yo niece at the weekend and relieving some of the 'Why? Why? Why?' constant line of questioning strain from her parents. She's just come into possession of a Slinky toy and was asking why (surprise!) it walks down the stairs in the way that it does.


Now telling her all about longitudinal compression waves, kinetic energy, momentum and gravity is just going to go over the top of her head and I don't want to respond with that all time classic default reply "It just does..." . I've told her that I'll 'ask my Engineer friends' (she knows all about you and that Engineers are very clever ?) and I know that she has the memory of an Elephant and will remind me next time I visit... ?


So.... How can I explain how a Slinky works in a way that a four year old would understand?
  • Not sure why you think concepts like longitudinal compression waves, kinetic energy, momentum and gravity should be beyond a four year old.

    It does need to be in the right vocabulary however.

    Here is a first pass, I suspect others can improve it.


    So, first what do we mean when we say something is springy ? Something about pushing on something and it pushes back, for example perhaps twang a ruler, or pull on some elastic or similar and show that you can change its shape, but it wants to change back, to relax.


    Well you start slinky at rest on the top step falling onto the next, and as the new pile builds up it gets squashed by the turns falling from the step above, energy is put in, and when the last turn has fallen, there is enough springy bounce to kick start the top turn into falling onto the next step down. But once that top turn is no longer holding the stack down, the next one down can bounce up too, and in turn each coil is both pushed up by springyness and pulled by the one that went before, the later turns mostly pulled.

    Meanwhile a new pile is building on the next step, ready to do it all again.


    This only works going down, as in a way it is getting the energy from falling, just  slowly. Falling uphill does not work simply from consideration of statistical averaging over all possible outcomes, as there are large number of similar  'down' positions, but only one 'up', so on average with any uncontrolled process things end up going down. - but exactly how that is a lesson for later in life, old enough to get a bit drunk and disable the controls that counter this entropy increase with effort, and keep the body upright.



    Edit next week try gyroscopic precession.

  • Thanks Mike! Very helpful. ?


    She's not yet four (will be shortly though) so she's still 3 in effect but you're right, she'll understand the concept just not the vocabulary used.
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    Refresh screen to get back to the begining.
  • Lol .... When you lob Tigger cartrolling down the stairs he bounces from step to step until he meets Eau....then its goodnight Tigger !

    perfectly understandable to a 3-4 year old...


    Legh
  • Oh BTW, the spring action works in tension as it has no potential in its compressed state without another force acting upon it....

    So when Tigger is bouncing from one step to the next step gravity, or the overwhelming desire to meet Eau, creates an energy causing Tigger to accelerate towards his great love.......???


    Legh