Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: clueless on 21/09/2012 19:48:02
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Physics isn’t my thing, but I’m working on a peculiar riddle. You see, there are two boxes in slope’s middle, as the boxes can’t slide down. I wonder if the boxes could slide if you put one on top of the other. If this is at all a possibility, what should the boxes and the smooth sliding surface be made of? And how heavy should the boxes be? And at which angle should the slope be, approximately, so that the above boxes start to slide down slowly ? Thanks. :-[
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Are you talking about the boxes above sliding of, or are you thinking that you want them all to start sliding down the slope?
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If you are talking about identical boxes on a particular gradient of slope, then whether or not they are stacked will make no difference, provided that both the box surface and the surface it is sliding over are dry and unlubricated. There will be a characteristic slope, at which sliding will start to occur. The critical gradient will depend only on the nature of the softer material.
The physics of the situation will be described in a good article on Amonton's Laws of friction. (unfortunately wikipedia gives a fairly inadequate account, and Adamson's "Physical Chemistry of Surfaces" might not be easy for you to find or access.)
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This is the way I visualize it, if this jpg makes any sense that is? :) Assuming boxes having flat surfaces following the slope. Then there must be a relation relative the slope it rests upon, box surface (friction), and gravity, as they get stacked, one upon another. If I assume that the question is about when the first box starts to move then sooner or later as you build upwards the angle becomes more acute, relative gravity's direction, and somewhere it (one of the boxes in the stack of boxes) must topple over. If we on to other hand assumes that the question is about if we can make them all move together as one, as that angle grows?
A human adjust automatically for gravity, going down a slope, by leaning backwards, but the stack of boxes shouldn't be able to do so :) We all exist on a endless slope, living on Earth, but macroscopically we find the ground 'flat' to us, at normal scales, with gravity right above us pointing towards the center of the earth, loosely speaking there, and it's also from that definition we think about slopes.
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Thinking about it again, won't it have a lot to do with the friction involved? So if I assume it to be a pole instead? Would it topple over, or would it move? As you 'stretch' that poles length out it becomes more unbalanced relative the surface, as I think? But, I'm not sure at all :) Da**
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Is it possible to change the coefficient of friction?
For example putting water on the slope?
Your friction coefficient will also be different for moving objects than non-moving objects, so giving them a slight push might help.
What about nailing your boxes into an inverted V shape?
[diagram=673_0]
Heat can also change the coefficient of friction. So, if you configure your boxes in a method to maximize the heat at the point of contact, that my in fact improve the sliding.