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https://www.youtube.com/watch?v=eLXHLRa37_g

In this video, we can see that rotating the paper somehow makes it less susceptible to being damaged. I can tell that the paper has some angular momentum. But how do we explain this phenomena in terms of energy transfer? It sort of remind me of how using simple equations, ( for momentum and energy) we can show that objects moving faster in a linear collision have less energy transferred to them. Is there an analogous description for 'rotating collisions'?

Moreover, would it be correct to say that the paper becomes harder when spinning very fast?

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  • $\begingroup$ I think it's less about "the paper takes less damage" and more like the "centrifugal" force makes the paper more rigid. A similar trick is to jam a straw into a potato: the straw buckles. But if you put your thumb over the end of the straw it is more successful because the trapped air in the straw adds rigidity. The limp paper was always sharp enough and strong enough to cut things, it just can't maintain its shape unless it is spinning. $\endgroup$
    – Paul B
    May 17 '17 at 20:27
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It is not just that the paper becomes hard, it is the friction that does the cutting. Angle grinders spin very fast, the glue and 3 pieces of paper add some rigidity and if you add that to the 'centrifugal' forces it is tough enough to cut through many things. I was surprised it did not burn with the wood, you could see smoke from that cut and the wood was burned on the surface of the cut.

As Paul B said in the comments above the paper could have cut all those materials without the grinder if you could just move it fast enough. The way it cuts is by removing a very small amount of material at a time, it just does it very fast due to the rpms.

Drew K

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