Why Do Vortices Pull Objects In? — A Challenge to the Bernoulli Explanation and a Multi-Origin Geometric Model

Abstract

Bernoulli’s principle is commonly used to explain why vortices draw objects inward, yet it only applies to two‑dimensional ideal steady flows or streamlines and cannot account for the three‑dimensional distortion, viscous shear, and sinking effects in real vortices. This paper proposes a geometric model based on an origin group, treating a real vortex as a hybrid of axial flow (line origin) and circulatory flow (single point origin). Its cohesive sinking force arises from the net potential difference generated by multi‑origin coupling. The model is consistent with physical observations and provides a unified description of axial flow, circulatory flow, and vortices.

1. Introduction: A Popular but Incorrect Explanation

- Many popular science texts and textbooks claim that the center of a vortex has higher flow speed and lower pressure, causing objects to be “sucked in.”
- Problem: Bernoulli’s principle holds only along a single streamline. In real vortices, streamlines form three‑dimensional spirals, and fluid at the vortex core and outer regions do not belong to the same streamline. Direct application of Bernoulli’s principle is therefore a misapplication.
- More crucially, pure two‑dimensional circulation (ideal vortex) produces an outward centrifugal effect and would only throw objects outward, never pull them inward.

2. My Core Model (Three‑Type Classification)

- Axial flow (line origin): Only axial thrust exists, with no rotation. Objects are carried downstream rather than pulled inward.
- Ideal circulation (single point origin): Only planar rotation occurs. Centrifugal force acts outward, while pressure acts inward (centripetal force), but objects with similar density to the fluid are not drawn toward the center.
- Real vortex (origin group): Superposition of multiple origins plus axial flow generates a cohesive sinking force, due to three mechanisms:- Viscous shear produces radial inward mass transport;
- Axial flow provides downward dragging;
- Multi‑origin coupling breaks centrifugal equilibrium and creates a net centripetal potential difference.

3. Why Bernoulli’s Principle Cannot Explain These Effects

- Bernoulli’s equation contains no viscous term and cannot describe radial mass transport caused by shear forces.
- Bernoulli’s equation assumes steady, irrotational flow valid along streamlines, whereas real vortices are rotational and undergo axial shear deformation.
- Applying a two‑dimensional ideal model to explain three‑dimensional viscous vortices represents a fundamental dimensional mismatch.

4. Consistency of My Model with Experiments and Observations

- Humans falling into water vortices are drawn inward: viscous shear combined with axial sinking produces a combined centripetal and downward force.
- Objects lifted in tornadoes: axial upward flow (the reverse of sinking) still relies on shear and origin‑group coupling.
- Light objects such as corks may concentrate near the vortex center due to dominant pressure gradients, but heavy objects being pulled inward additionally require viscous effects.

5. Conclusion

Bernoulli’s principle does not provide the correct explanation for vortex suction. The proposed MOC multi‑origin model offers a more realistic and geometrically consistent understanding.