Once the ideas have been tossed around, students will be wondering how to choose between all of these concepts. They should be encouraged to formulate questions and experiments that will help to answer them. There is a natural tendency to go for the ideas the one likes best, or has a "gut" feeling for. These concepts may indeed be the ones that work out best, but unless they are tested against other concepts, the designer can never be sure that all ideas were investigated fully and the best design was selected.

There are many ways to investigate ideas, such as research and consulting with "experts", but the most direct and convincing way is to try it out for oneself. This is the essence of hands-on design. Often the design is broken down into smaller problems which are investigated individually. In the case of a model solar car, the "smaller problems" are the individual mechanical components (wheels, transmissions, chassis, etc.).

Some possible investigations are:

The investigations called for here are likely to be simple experiments where students get a feel for the mechanical concept behind their question. A complex investigation may be broken up and assigned to different groups or individuals; their results can later be shared with the entire class. A student investigating materials and methods for building a car chassis, for example, may take simple pieces of each material and watch how they react to various loads or forces. Another example may be to build various transmissions on a simple chassis (not necessarily the one they intend to use in their final car) and compare their relative performance and ease of construction. As part of this process, students should identify design variables, that is, attributes which can be varied to affect performance.

Some of those design variables are:

The goal of these investigations is to gain an understanding of all the individual parts of a vehicle. The groups will probably have a few concepts for each component; they will be narrowed down in the next phase.