3 ms·
Is this simply because the coefficient of friction between two surfaces is typically smaller when the surfaces are in motion than when they are at rest? If you
by jschwartzi 10y ago
Is this simply because the coefficient of friction between two surfaces is typically smaller when the surfaces are in motion than when they are at rest? If you wanted to reverse the insertion of a peg into a hole, you would have to halt it's motion for an instant, and at that point in time I would imagine you have to overcome static friction to make it move in the opposite direction. Friction forces can be dependent on the normal force between the two surfaces, so it's possible to jam a peg into a hole so that you can't get it out.
- jmount 10y agoUnfortunately it is merely a math problem. Until the peg comes in contact there is no friction. After it is in contact there is friction, and if the geometry is just wrong enough "virtual forces" to oppose any force. Real matter (which bends) can't have this problem- it is from the rigid model. The non-reversaiblity is this flaw plus the fact there is no friction in the model prior to contact (so there is a non-reverisble feature in the model).
- jschwartzi 10y agoIt makes sense. After all, in real life I would just wiggle the peg to "walk" it back out of the hole, and that only works if the body is not perfectly rigid, and no body is perfectly rigid.
- static_noise 10y agoIn reality your body could have barbed hooks which insert easily but dig into the walls when you try to pull it out. Wiggling doesn't help there.
- lostlogin 10y agoI'm currently repairing some 1940s windows and replacing the hinges. I can say with confidence that some things are completely rigid and will never be moved despite use of hand and power tool. Old hardwood and steel construction.