An old-fashioned record player spins a disk at approximately a constant angular velocity, w. A fly of mass m is sitting on the disk as it turns, at a point a distance R from the center. a) What force keeps the fly from sliding off the rotating disk? What direction does it point? How big is it? For the last question, express your answer in terms of the symbols given in the description above b) If the fly has a mass of 0.5 grams, is sitting 10 cm from the center of the disk, and the disk is turning at a rate of 33 rpm, what is the coefficient of friction?

A professional scientist (not a physicist) once stopped me in the hall and said: "I can prove Newton's theory of gravity is wrong. The sun is 320,000 times as massive as the earth, but only 400 times as far from the moon as the earth is. Therefore the force of the sun's gravity on the moon should be twice as big as the earth's and the moon should go around the sun instead of around the earth. Since it doesn't, Newton's theory of gravity must be wrong!" What's the matter with this reasoning?