static friction explained
Friction is the force a surface raises against sliding, and it changes its own size to match the force pushing the body. Only up to a limit, and F ≤ μs N is that ceiling, and past it the body breaks free and slides. It holds just as much as it needs, and lets go once the limit is passed.
Drag the pushing force and the friction quietly grows by the same amount and holds the block. It is self-adjusting, and the block slides only once the push passes μs N. Until then it pushes back exactly as much as you push.
That limit is Fmax = μs N, set by the normal force pressing the surfaces together. Pile on more load and the surface can hold more, and dragging the normal force shows that relation as it stands. Press harder and the ceiling rises with it.
Static friction can climb up to μs N, but once sliding starts it drops to the smaller kinetic value μk N. That sudden drop is the lurch you feel when a stuck body breaks free, and the toggle shows the gap between the two values. While it moves, the smaller value is what remains.
Tilt an incline and the block holds until the slope reaches the angle where tan θ = μs, and then it slides. That angle has nothing to do with the weight, and dragging the angle shows where the limiting angle sits. A heavy block and a light block break free at the same angle.
Behind that sits the friction angle φ. It is the angle where tan φ = μs, and the total reaction of the contact, the normal force plus the friction, can lean at most φ away from the normal of the surface. When the lean reaches that, sliding starts, and dragging the coefficient moves the limit with it. One angle stands in for the roughness of the surface.