Final answer:
According to Newton's First Law, a penny placed on a surface will remain at rest due to its inertia. When the surface is moved away and with little friction between them, the penny drops vertically into the cup because of the gravitational unbalanced force acting upon it.
Step-by-step explanation:
Newton's First Law of Motion and the Falling Penny
Using Newton's First Law of Motion to describe why the penny falls into the cup, we must consider the concepts of friction, inertia, and balanced and unbalanced forces. Newton's First Law, often referred to as the law of inertia, states that an object at rest will stay at rest, and an object in motion will stay in motion with a constant velocity, unless acted upon by a net external force. In the scenario involving a penny and a cup, when the cup is quickly moved away, the penny demonstrates inertia; it remains in its state of rest relative to the moving cup. Because there is little to no friction between the penny and the surface it was resting on (presumably paper or card), the unbalanced force, which is the sudden movement of the cup, leads to the penny dropping vertically into the cup below.
Understanding that friction acts in the opposite direction of motion is crucial to this concept. If a ball moves north to south, for example, friction would act in the south to north direction, going against the direction of the ball's motion and eventually slowing it down. However, in the case of the penny, the lack of significant friction prevents it from moving with the cup when it is pulled away, leading to the penny's vertical fall due to gravity, which in this case is the unbalanced force.