Saturday 11 May 2013

The Madness of the Inclined Plane

I wrote just now about the humiliation of failing my Physics "O" level.  I'm not stupid, my folks paid a great deal of money to send me to a school that had above average science teachers - one of whom started me off on a lifetime embedded in science.  But there were elements of what physicists know that were plainly bonkers and so my rational head revolted at having to embrace them.  The analysis of the forces involved in a block (or a car, a wheelbarrow, a bloke) sitting (or sliding or just about to slide) on an inclined plane is a standard problem for teenage would-be physicists to tackle.  So standard indeed that I had a choice of hundreds of pictures of the problem to loot off the internet.  The wee arrows show the forces that have to be considered: f(k) is something to do with friction which normal folks kind of take for granted and ignore but which can be explained by pointing out that a block tends not to slide down a slope while a ball of identical weight does.  So that's a useful insight.  And of course the block is pressing down on the inclined plain - because that's gravity and it would be a shockin' shame if Isaac Newton had lived, and his pet apple had died, in vain.  And because physicists tend not to be math-anxious, I can sort of understand why they might want to resolve the force W into two vectors (I think W.sinθ and W.cosθ are called vectors and maybe W is a vector too) so that they are at right angles to the plane.  So the block is pressing down on the inclined plane (tick, gottit) but physics expects us to believe that the inclined plane is pushing back on the block!  See what I mean?  Daft.

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