Final answer:
True. The force of friction opposing motion is indeed always opposite to the direction of motion of the object. This is a central concept in understanding the resistance provided by frictional forces, which act to oppose both actual and attempted movement between surfaces in contact.
Step-by-step explanation:
The statement that the force of friction always acts on all moving objects and is opposite to the direction of motion is true. Friction is a resistive force that opposes both motion and the tendency toward motion between two surfaces in contact. When an object is already in motion, the frictional force acts in the direction opposite to that of the object's movement, which can be observed by the slowing down of a moving object when no additional force is applied.
For instance, if someone is pushing a crate across a floor with a specified force, the force of friction must be in the opposite direction to prevent acceleration. This ensures that the net force (Fnet) acting on the moving crate is zero for constant velocity, as per Newton's first law of motion. Thus, for example, if the applied force is +50 N to the right (positive direction), the frictional force must be -50 N to the left (negative direction), resulting in no net force and thereby maintaining constant velocity.
The behavior of friction is complex and is influenced by the roughness of the surfaces in contact and the molecular forces between them. Even when the surfaces appear smooth, microscopic interactions and molecular attractions contribute to the creation of friction.