00:01
Hello, if we picture our plane looking like this, angle theta with our mass, here its weight is mass times gravity, the component of weight along the plane is mass times gravity sine theta, and the component perpendicular to the plane is mass times gravity cos theta.
00:28
There is reaction r and there is friction mu r.
00:33
Now for this to be in equilibrium or just about to move, the forces along the plane must balance, so mu r equals mg sine theta.
00:49
Similarly, forces perpendicular to the plane must balance, so r equals mg cos theta.
00:57
Now we divide both sides and so we have mu at the left hand side being equal to this cancels out and sine theta over cos theta is tan theta which is tan 15 which is 0 .27.
01:34
So then if there is acceleration, that is coefficient of static friction.
01:48
Now if there is acceleration, then that acceleration is along the plane which means that the positive force here is mg sine theta and the friction is the force opposing the motion as usual, mu mg cos theta because friction is mu r and from this place or from the second equation we know that r equals mg cos theta.
02:17
So if friction equals mu r, then friction is simply mu mg cos theta...
