in high school , i solve friction questions by making FBD but recently i got a doubt while imagining a situation
suppose there is a block of mass 4kg kept on ground and we apply a force of 20N and lets assume the limiting friction is 14N and kinetic friction is 12N , so the block will start sliding and when we make equation of motion for this block we will get
20N – 12N = 4a
a = 2m/s²
so the block will have acceleration 2m/s²
but if we think of what will happen after our force, the block will stop after sometime
so what does actually happen after this 2m/s² acceleration which causes the block to stop , it will be friction obviously ( if we neglect air resistance ) but does friction keep resisting the motion of block and if yes then can anyone explain thoroughly what exactly happens cause this was never taught in our class ,
thanks
In: Physics
Friction is only a reactionary force. It helped me to think that it only exists to oppose motion, so when there is nothing trying to cause motion, there will be no force of friction. So when the block comes to rest, the static friction is zero until additional force is applied, and then it is a force up to the maximum (14N in your example). But the force of friction is 12N until the block does come fully to rest, at which point it becomes zero until additional forces are applied. Once the block is stationary, the static force is whatever it needs to be to make the block stay, up to 14N. So if you apply 10N, it will push back 10N, 11N -> 11N, etc.
I think that’s what you’re asking at least? If that wasn’t what you were asking or if you need more clarity let me know and I can try to elaborate
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