Which of the following is true about friction? O In any problem with static friction, we can assume the size of the static frictional force is its maximum value fs, max- O It is harder to get an object to move along a rough surface because it has higher coefficients of friction than a smoother surface. The kinetic frictional force fx can change size to match an applied force. The kinetic frictional coefficient up between two surfaces is generally larger than the static frictional coefficient us between them