2️⃣CAUSES of FRICTION 🛑How does friction work on a microscopic level?

Why does static and kinetic friction opposes motion. There are 2 causes of friction. But before we answer that question, we need to ask "What is friction in physics?

Take a regular polished surface and see it under a microscope, this is what you see it is far from being flat. When two such surfaces are placed together, only the high points like these come in contact and then many atoms of both surface contact each other, and the surfaces cold-weld together, and these welds are what produce static friction. So, when an applied force attempts to slide a surface, there is first a tearing of welds and then a continuous re-forming and tearing of welds as motion occurs.

If the two surfaces are pressed together harder, many more points cold-weld and that is the reason we say - greater the Normal force, more the friction…this is reason number 1

The second reason is interlocking of these peaks and valleys on the surfaces in contact and rough surfaces have larger number of such irregularities and therefore the surfaces offer more friction as compared to smooth surfaces.

In summary, How does friction work on a microscopic level?

1. _Microscopic Irregularities_: When two such surfaces are in contact, they cold-weld at these high points, creating what we call static friction. This is the first reason for the occurrence of friction.
2. _Interlocking of Surfaces_: The second reason is the interlocking of these microscopic irregularities.

#neetphysics #jeephysics #apphysics #class11physics

[DeepGraphics]

Sir why only upward normal in considered while calculating friction if the downward normal is the one which pushed the upper surface down, please answer this sir