* Newton's First Law: An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
* To start motion: You need to apply a force greater than the forces opposing it (like friction). This creates an unbalanced force.
* To reach 0.5 miles per second: The force you apply must overcome the forces of friction, and continue to accelerate the box until it reaches that speed.
In other words: If the forces were balanced, the box would either stay at rest or continue moving at a constant speed. To get the box moving and accelerating to 0.5 miles per second, you need to apply a stronger force than what's resisting it.
