Assertion: The step prior to a "prep for ROP" must have CBM, since ROP is both a Dance Position and a Step Alignment

✅ Definition Breakdown

1. ROP (Right Outside Partner) is both:

• A Dance Position: where the partner steps outside their partner’s right side.
• A Step Alignment: requiring the foot to land in CBMP (Contra Body Movement Position), and the torso to rotate to accommodate this placement.

This duality means ROP cannot be achieved through foot placement alone — the upper body must contribute.

🔍 Analysis of the Prior Step

Example: Feather Step (Foxtrot, Leader)

• Step 1: RF forward — marked “no turn,” but CBM is explicitly included in syllabi.
• Step 2: LF forward, L side leading — labeled “prep ROP.”

Why CBM on Step 1? It initiates body shape needed for ROP on Step 2. Without it, there’s no space for the partner to pass outside.

Example: Back Feather (Foxtrot, Follower)

• Step 1: LF back — often marked “no turn.”
• Step 2: RF back in CBMP — ROP.

Biomechanical Insight: Even on a backward step, a slight rotation of the torso (CBM-lite) is necessary to clear a path for the Leader’s ROP.

🚫 Disproof Attempts & Failures

Could ROP be entered without prior CBM?

• No, unless frame breakage or foot collisions are acceptable.
• Without CBM, the partner would step directly into the closed body line.

The physical impossibility of occupying the same space proves the necessity of CBM to create that space.

✅ Conclusion

The step prior to a "prep for ROP" must have CBM, even if not formally listed, because ROP is a combined spatial and rotational requirement.

This assertion is biomechanically undeniable:

• The feet cannot get there without the torso.
• The torso cannot prepare without CBM.

Assertion stands. ✅

Outside Partner Dynamics & The Inertia Bleed Model

🧭 Objective

To analyze and model the biomechanics of Outside Partner (OP) figure endings in ballroom dance — especially those like the Feather Step — where dancers do not close their feet. These figures naturally create residual momentum, rotational energy, and thus, biomechanical consequences that affect the start of the next figure.

🔬 Theoretical Model

Key Assumptions

• Velocity (linear) is negligible at end of step 3 — rotational energy dominates.

• Only figures ending with feet apart (OP/PP/CBMP) are relevant.

• Final angular displacement over Δt (default 0.5s, 1 beat in Foxtrot) defines the residual inertia.

• Center of mass rotates at radius r ≈ 0.3m from spine.

  💡 Key Insights

• The end of a figure is the beginning of the next — and carries biomechanical baggage.

• CBM should be treated as a curve that occupies an entire beat.

• Sway during the step (e.g., right sway in Feather) can dampen residuals.

• Closing steps (e.g., Natural Turn 3) tend to dissipate energy cleanly