Question

why is it always harder to start to move an object that is initially at rest across a horizontal surface than it is to keep that same object moving?
a the static friction between two surfaces is always greater than the kinetic (sliding) friction between the same two surfaces.
b the amounts of static friction and kinetic (sliding) friction must add up to cause the object to accelerate.
c an object that is at rest has more inertia than on object that is moving.
d the lack of a normal force once the object is moving requires less effort.
e the static friction and kinetic (sliding) friction are always equal in size and opposite in direction.

Explanation:

Static friction resists the start of motion and is greater than kinetic friction which acts during motion. Once an object is moving, less force is needed to overcome kinetic friction compared to the static friction needed to initiate movement.

Answer:

A. The static friction between two surfaces is always greater than the kinetic (sliding) friction between the same two surfaces.