Drummer_Dave

I read that learning to use an abacus can help with one's own mental arithmetic... anyone experienced this? And any suggestions of a good abacus (type) to buy? Thanks in advance..

You were right, I tried in in daylight and the shape nor direction didn't appears to change, it stayed as a many sided polygon, close to a circle (the daylight is not great at the moment). Thanks again for your replies.

Thank-you Halc, that sounds very feasible. Only tried under LED lights, will try tomorrow in natural light. Great answer, thank-you. Obviously I'm aware that the direction of spin doesn't change, and its now quite clear that it is the precession idea that suggests a direction of rotation (thanks again). Taking it in reverse, imagine a 3cm slice of a pringle tube on the table, starting to spin increasingly fast. As it starts to spin, it slowly rotates on one edge and goes from a horizontal plane to almost vertical. But it's the top down view as it's spinning almost vertically.... why does the inner space created by the body of the ring briefly form regular polygons with increasing number of sides?

So, I'm spinning my wedding ring on the table, (I'm right-handed, so spin it anti-clockwise, with my right thumb on the bottom and my left forefinger on the top). If I look down on it from above, it goes through a number of phases (has to be spun quite fast): 1. starts spinning anti-clockwise 2. the centre forms a triangle shape 3. slows and starts spinning clockwise 4. slows and starts spinning anti-clockwise and the centre forms a square 5. slows and starts spinning clockwise 6. slows and starts spinning anti-clockwise and the centre forms a pentagon 7. slows and starts spinning clockwise 8. slows and starts spinning anti-clockwise and the centre forms a hexagon.. ..etc. Can anyone explain to to me please?

Why don't firefighters use crushed dry ice, or just CO2 to help fight bush or moorland fires?