‘Two identical bolts are placed together so that their helical grooves inter-mesh as shown in the illustration. If you move the bolts around each other as you would twiddle your thumbs, holding each bolt firmly by the head – so that it does not rotate – and twiddling them in the direction shown, what will happen to the heads?’
Will the heads (a) move inward, (b) move outward, or (c) remain the same distance from each other?
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