The best explanation for why your body continues to move forward when you trip is: An unbalanced force stops your foot but does not act on the rest of your body.
When you trip, the ground exerts an unbalanced force on your foot, bringing it to a sudden stop, while your upper body, due to inertia, continues moving forward until it catches up with your foot. This situation illustrates Newton's First Law of Motion, which states that an object in motion will stay in motion unless acted upon by an unbalanced force.