Final answer:
The magnitude of the friction force varies based on the normal force, applied force, and the weight of the object; therefore, all of the above forces affect it.
Step-by-step explanation:
The magnitude of the friction force is directly related to specific forces acting upon an object. These forces include the normal force, the weight of the object, and the applied force. The friction force comes in two forms: static friction, which operates when there is no motion between the objects, and kinetic friction, which comes into play when the objects are moving relative to one another. The force of friction depends on the coefficient of friction between the materials in contact and the normal force exerted by the surfaces on each other. In summary, the magnitude of the friction force varies depending on the normal force, applied force, and weight of the object; this is why the correct answer is 4) All of the above.