Quote:
Originally Posted by Ragingmain
I guess one more way I can put it is this. If you had to move a piece of 4x8 plywood and could not carry it and the only two options you had were to
1. Lay it on the ground flat and try to push it?
or
2. Lay it on its edge and push it?
Same amount of weight. one has a bigger contact patch then the other. Which one will be easiet to move?
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With your mechanical engineering degree, you should absolutely know why this situation is totally different than traction of a wheel applied to the ground.
First of all, you're attempting to make an argument not based on physics, observation, or empirical data, but on intuition. You're basically saying "doesn't it seem like this would be harder?". You're creating a contrived example and implicitly asserting that the reason one technique is harder than the other is *entirely* friction. Intuition is not how to make an engineering argument.
Second, I'm going to challenge the implicit assertion that the differences in force are due to friction entirely. A thin sheet of plywood is not flat - it's going to dig into the likely deformable surface it is under, such as carpet. For example, an edge could get caught in some carpet fibers. Putting a piece of plywood on its edge helps in part because there is so much less area for the plywood to "catch" the surface on. On a perfectly smooth surface, with smooth plywood (equal surface treatment on the edges and the flats), I don't believe there would be nearly as dramatic a difference.
Finally, the scenario you described does not even relate to wheel traction! The contact patch of an ideal wheel that is not slipping is stationary relative to the ground. Static friction is the phenomenon in play in this case. When pushing a flat piece of wood across the floor,
dynamic friction is a factor for a vast majority of the time you're pushing the wood. Dynamic friction can depend on surface area / contact patch much more than static friction does.