What effect does friction force have on motion?
a. It opposes the motion of all objects.
b. It counteracts the acceleration of an object
c. It prevents surfaces from sliding against each other.
d. It causes objects to accelerate.
Friction can be defined as the force that resists the relative motion of solid surfaces, fluids, or elements that collide or slide against each other.
Its effect would cause the object in motion to slow down. If the friction is increased, more energy is needed by the object to keep its momentum hence it will slow down.
It does not oppose all the motion of object neither does it counteract the object to accelerate. It does not prevent the objects from sliding with each other because friction will only exist if two materials slide against each other. The best description would be that as the collision happens, the energy (kinetic) will increase thus accelerating the object. So friction in totality can cause the object to accelerate.