Note that, if you reduce the tilt of the surface (that is, make θ smaller), the cosθ term in Equation (???) grows and the sinθ term gets smaller, so we must ma...Note that, if you reduce the tilt of the surface (that is, make θ smaller), the cosθ term in Equation (???) grows and the sinθ term gets smaller, so we must make sure that we do not use this equation when θ is too small or we would get the absurd result that ax < 0, that is, that the force of kinetic friction has overcome gravity and is accelerating the object upwards!
