What is hypothesis testing

Why is there friction between objects

A0.580-kg rock is tied to the end of a string and is swung in a circle with a radius of 0.500 meters. the velocity of the rock is 4.50 m/s. what is the centripetal force acting on the rock? 15.5 n 5.22 n 69.8 n 23.5 n

Matter is needed to transfer thermal energy bya. conductionb. convectionc. radiation d. both a & b.