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
You got it right, the kinetic friction is going to apply as long as that block is in motion. That’s why if you throw a book across the floor it eventually stops.
The issue is that pushing a block across the floor is actually two different problems. The first problem is more complicated and happens when the block has a force applied to it. The second problem is often ignored because its much simpler. You’ve identified the transition from problem 1 to problem 2 and that problem 2 is different.
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