Friction . 1.happens whenever work is done
2.occurs when objects rub against each other
3.releases energy as heat
4.all of the above

What is magnetic flux? explain faraday's law of induction.

At a certain instant after jumping from the airplane a, a skydiver b is in the position shown and has reached a terminal (constant) speed vb = 52 m/s. the airplane has the same constant speed va = 52 m/s, and after a period of level flight is just beginning to follow the circular path shown of radius ρa = 2330 m. (a) determine the velocity and acceleration of the airplane relative to the skydiver. (b) determine the time rate of change of the speed vr of the airplane and the radius of curvature ρr of its path, both as observed by the nonrotating skydiver.

Ajoint produces movement when its angle decreases. which type of movement is it?