Cos(2θ) = cos²θ - sin²θ = (1-sin²θ)-sin²θ = 1-2(7/9)^2 = -17/81
Friction is the resistance to motion of one object moving relative to another. It is not a fundamental force, like gravity or electromagnetism. Instead, scientists believe it is the result of the electromagnetic attraction between charged particles in two touching surfaces.
He displays a physical response because his head moves
He displays engaged listening because he is humming along
