Creating contrast between rigid and fluid forms is a powerful design technique that can elevate visual interest and dynamic balance in any artistic or architectural project. Here are the most effective ways to achieve this striking juxtaposition:

1. Material Selection: Pair rigid materials like steel or concrete with fluid materials such as glass or fabric to emphasize their inherent differences. The hardness of metal against the softness of draped fabric instantly creates a compelling contrast.

2. Geometric vs Organic Shapes: Combine sharp, angular structures with smooth, curvilinear forms. This approach is widely used in architecture, where rectangular buildings are softened by flowing landscape elements or sculptural installations.

3. Light and Shadow Play: Use lighting to highlight the differences between rigid and fluid forms. Harsh directional lighting can accentuate rigid edges, while diffused lighting enhances fluid forms' gentle transitions.

4. Scale and Proportion: Exaggerate the scale difference between rigid and fluid elements. A massive, blocky structure paired with delicate, winding pathways creates an unforgettable visual tension.

5. Texture Contrast: Juxtapose rough, textured surfaces with smooth, polished ones. The tactile difference reinforces the visual contrast between rigid and fluid elements.

6. Color and Tone: Employ contrasting color schemes - cool, muted tones for rigid forms and warm, vibrant hues for fluid elements, or vice versa, to strengthen their distinct characteristics.

7. Movement Implication: Design rigid elements to appear static while fluid forms suggest motion, even in static displays. This can be achieved through strategic positioning and form language.

The most successful implementations of this contrast principle maintain an underlying harmony, using repetition of materials, colors, or design motifs to unite the disparate elements. When executed well, the tension between rigid and fluid forms creates spaces and artworks that feel both dynamic and balanced, engaging viewers on multiple sensory levels.

Remember that effective contrast isn't about opposition but about complementary relationships that highlight the unique qualities of each form type while creating a cohesive whole. This principle applies equally to graphic design, product design, architecture, and fine art.