Misconception : Friction always opposes motion
Corrected Version : Friction always opposes ‘relative‘ motion. Relative is the word which most of the people miss and this creates the whole confusion.
But, how can we explain this concept in a much clearer manner ? – We are going to do this in today’s short but important article
Explanation :
Analogy for better understanding :
You can imagine this scenario as a teacher controlling a small group of students on a picnic. The teacher strictly instructs that “No student should try going forward and no one should be left behind. Stay Together”
- In physics terms, what she means is : There should be no relative motion between any student i.e. all should move as a unit
Having an idea of this, we are in a postition to answer the following question below :
Case 1 : if (v1 > v2)
Then the direction of friction on the block will be forward while that on the surface will be backward. This is because :
- As the surface moves faster, the block will say to surface, “Hey, be with me…you are too fast”. Hence it tries to oppose surface
- While, as the block moves slower relatively, the surface will say to block, “Hey, be with me…you are too slow…I will support you”. Hence, friction gets applied in forward direction for the block
Case 2 : if (v1 < v2)
Then the direction of friction on the block will be backward while that on the surface will be forward.
Case 3 : if (v1 = v2)
There is no friction between the block and the surface as there is no relative motion between the two
