Question

why isn't it accurate to say static friction is the force that keeps objects from moving? describe a counter example like a box on a table

Answer 1

Hello

Consider a box is placed on a table . when we apply very little amount of force on it it won't move because an equal and opposite force is generated which prevent the motion of box, this force is static fictional force. When we increase applied force on block ,static friction increase accordingly to prevent motion but when applied force increases further ,a point is reached when the opposing force reaches a limit and the box starts to move. Here frictional force acts as a opposing force.

Now consider another example , a man walking on a road. To move on a road we have to apply some force on road and due to this frictional force comes into picture. But the question is "in which direction frictional force acts? ". When we walk we pushes the road with the help of our legs. We apply force in opposite direction of motion due to which static frictional force arises in the direction opposite to that of applied force i.e in the direction of motion. Thus helping us to move in forward direction. Our leg wants to move backward and friction keeps it stationary by acting in forward direction .This frictional force balances the applied force and helps us to walk. If there is no frictional force is acting, our legs will slip off and we are unable to walk. Hence it is not accurate to say that static friction is the force that keeps objects from moving . Here in this case frictional force is supporting the motion.