1R10  Hooke's Law
            .10 Hooke's Law
1R20  Tensile and Compressive Stress
1R30  Shear Stress
1R40  Coefficient of Restitution
            .10 Bouncing Balls
            .30 Dead and Live Balls
1R50  Crystal Structure
            .20 Bravais Lattice Models
            .20 Crystal Models