Final answer:
To initiate motion in Tim, one would have to apply an external force, as per Newton's First Law of Motion.
Step-by-step explanation:
To get Tim in motion you'd need to exert an external force on him. The correct answer is therefore option A: External force. This is a statement about inertia that describes how it is necessary to use force to change an object's state of motion. Friction, as defined by physics, is a force that opposes the motion of objects sliding past each other, and while it is an external force, specifically referring to getting Tim in motion would mean overcoming static friction to initiate motion. An impulse involves a force applied over a time interval, and while it changes the momentum of an object, in this context, simply the term 'external force' is more appropriate and more directly answers the question.