Tension (the pulling forces on materials) and compression (the pressure on materials), give many structures a floating effect. For Lego lovers, you can try suspend portions of structures by creating your own arches and bridges. Truss bridges, in particular, use tension and compression to get the job done. It's also important to keep in mind your material's stiffness, as it will give more or less when under additional pressure.
Click ahead for more tips on structural engineering of the Lego variety.