Leonardo da Vinci Bridge Physics Demonstration Kit, 5 Foot Span Base Size_8 x 5" Slidable electromagnet on this 6V Slidable electromagnet on this 6V drive lets students vary amplitude while the chrome plated steel prongs (10 x 25 x 300mm) sustain an accurate 60Hz vibration on a horizontal or vertical base Twelve place hardwood test tube rack combining ten 19 mm holes and two 25 mm holes with twelve draining pins for mixed size storage and inverted drying on the bench demonstrating how friction and gravity balance lateral and gravitational forces in an arched truss Leonardo da Vinci self supporting bridge kit spanning five feet without tools or glue