The amazing rattle back

 

Many of you probably know what a rattleback is but I only found out about them recently. My other half learned about them from watching an episode of QI and was fascinated enough to buy us both one. I am the proud owner of this yellow one you see pictured here. as you can tell, it is a boat shaped piece of plastic. Those of you who are in the dark about this toy as much as I was may be wondering what is so remarkable about it. So let me tell you. it has a preferred spin direction. If you spin it in one direction it will happily spin away until it has gradually lost all of its kinetic energy due to friction and as you might expect then stops. However if you try to spin it in the opposite direction, it will resist and rattle about dramatically before then reversing its spin and once again happily rotating in its preferred direction.  This appears to violate the law of conservation of angular momentum which states that the amount of rotation an object has depends on its mass, shape and speed and this remains content if no external torque is applied to the object.
So this makes the rattleback a curiosity which has excited human imagination since prehistoric times. Indeed it is also known by several other names including "celt' ''celtic stone'' and ''space pet''.

here is a youtube video showing this effect somewhat dramatically on a much large rattle back.

This is a great video but doesn't really explain the effect and I haven't done so in any great detail either. I will say rather teasingly that I leave you to think about it or look it up yourselves. If you are a physicist, then perhaps, you know already and can explain it much better tan i ever could. I hope however that you enjoyed this post. Please let me know in the comments :)