# Project: Designing a Virtual Bridge

There are an abundance of simple, yet though-provoking problems involving Newton's Laws. Two of my favorites:

• If the earth is pulling me down with gravitational force, what is providing the equal and opposite force stipulated by Newton's Third Law? (Hint: it is not the ground pushing up on me, since the earth is pulling on me whether I am touching the ground or not).
• When a car accelerates, what is the providing the external force that accelerates the car? (Hint: it is not the engine, or the tires, both of which are part of the car)

Note that both of these problems require qualitative answers. Although physics is often associated closely with mathematics, the student should also be able to understand its basic laws without drumming out a quantitative example.
Indeed, once a student has mastered the ideas and the mathematics, it becomes clear that the number of forces involved in a real problem can be large, and we haven't developed all the tools we need to solve the mathematical piece of the problems. Yet, we want to be able to look at a realistic problem.
The West Point Bridge Designer provides a nice way to look at a complicated structure and understand the forces in both a qualitative and quantitative way, and we have a project based on the program.