A tabletop demonstration of distributed friction: the spinning wine glass

Ruben Canora

REVIEW 1 major objections 1 minor 6 references

Dragging a wine glass along a circular path on a table causes spontaneous spinning from uneven friction due to pressure redistribution.

Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →

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T0 review · grok-4.3

2026-06-27 02:34 UTC pith:2LX4ELEB

load-bearing objection The symmetry of pressure shift under a centered force means no net frictional yaw torque is generated, so the central claim does not hold. the 1 major comments →

arxiv 2606.20694 v1 pith:2LX4ELEB submitted 2026-06-15 physics.class-ph physics.pop-ph

A tabletop demonstration of distributed friction: the spinning wine glass

Ruben Canora This is my paper

classification physics.class-ph physics.pop-ph

keywords wine glassdistributed frictionfrictional torquepressure redistributionspontaneous rotationcircular dragtabletop demonstration

verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper derives equations for a wine glass dragged in a circle that begins rotating about its vertical axis even without twisting force from the hand. The cause is the hand force shifting how pressure is distributed under the base. This shift creates stronger friction on one side than the other, producing a net torque. A sympathetic reader cares because the demonstration shows ordinary friction can generate rotation through everyday mechanics in a simple tabletop setup.

Core claim

When a wine glass is dragged on a table along a circular path, a spontaneous rotation about its vertical axis can develop even if the applied hand force does not directly introduce a yaw torque. The mechanism responsible for this effect is the redistribution of pressure onto the table when applying the force with your hand. This causes an uneven frictional force distribution which exerts a torque on the glass, causing it to spin.

What carries the argument

Redistribution of pressure across the glass base that produces an uneven frictional force distribution and net torque

Load-bearing premise

The applied hand force produces a pressure redistribution across the glass base that is sufficient to generate a net frictional torque without any direct yaw component from the hand.

What would settle it

The glass fails to spin when dragged in a controlled circular path while pressure under the base is kept uniform, or pressure measurements show the redistributed friction yields zero net torque.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

The spinning arises solely from the torque of uneven friction without direct hand yaw.
Governing equations derived from the pressure redistribution predict the observed rotation.
The effect occurs specifically in circular dragging paths where hand force offsets the contact.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

The same pressure-friction mechanism could produce spontaneous rotation in other round objects like plates or bowls under similar dragging.
Varying the hand force location or base material in experiments would test how strongly the torque depends on pressure shift.
The model supplies a simple way to illustrate distributed forces in classroom settings using only a wine glass and table.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Desk Editor's Note

The symmetry of pressure shift under a centered force means no net frictional yaw torque is generated, so the central claim does not hold.

read the letter

The paper offers a tabletop demo of a wine glass spinning while being dragged in a circle and attributes it to hand force redistributing base pressure, which then creates uneven friction and a net vertical torque without any direct yaw from the hand.

The demo itself is straightforward and the attempt at a formal derivation is clear enough on the surface. That part could be useful for showing students how contact forces act over an area.

The load-bearing problem is the symmetry issue. A force applied through the center with no yaw component only varies normal pressure along the direction of motion. The base stays symmetric perpendicular to that direction, so the integral for frictional torque about the vertical axis cancels: the contributions from left and right sides are equal and opposite. Breaking that left-right symmetry requires an offset in the force application point, but any such offset immediately supplies a direct yaw moment from the hand force itself. The abstract explicitly rules out direct yaw, which leaves the claimed mechanism without a way to produce the torque.

Nothing in the description indicates the derivation accounts for this or introduces additional effects that would break the symmetry. The result therefore reduces to a standard rigid-body friction model that does not generate the spontaneous rotation under the stated conditions.

This is the sort of note that might interest someone collecting classroom examples, but the analysis does not check out. I would not bring it to a reading group, would not cite it, and would not send it for peer review without a major rewrite that either drops the no-yaw assumption or shows why the symmetry argument fails.

Referee Report

1 major / 1 minor

Summary. The manuscript describes a tabletop experiment where dragging a wine glass along a circular path on a table induces spontaneous rotation about its vertical axis. The central claim is that this occurs via redistribution of normal pressure from the applied hand force (without direct yaw torque), producing an uneven frictional force distribution that generates net torque. The paper provides a structured formal derivation of the governing equations to support this mechanism.

Significance. If the result holds, this would constitute an accessible demonstration of how distributed contact forces can produce unexpected rotational dynamics through friction alone. It could serve as an educational example in classical mechanics for illustrating torque from non-uniform normal loads, with potential value for classroom or outreach activities. The attempt at a formal derivation is noted as a strength in principle.

major comments (1)

[Abstract and governing equations derivation] Abstract and main derivation: the claim that hand force without direct yaw torque can produce net frictional yaw torque via pressure redistribution is load-bearing but appears internally inconsistent with symmetry. A centered force Fx produces moment about the transverse axis and N(x) variation, but preserves N(x,y)=N(x,-y); thus τ_z = μ ∫ y N dA vanishes identically. Any lateral offset that breaks y-symmetry simultaneously supplies direct yaw torque via r × F. The derivation must explicitly show how the claimed mechanism evades this without reducing to direct torque or fitted parameters.

minor comments (1)

[Abstract] The abstract would benefit from stating the key assumptions (e.g., force application point, contact model, whether the circular path introduces additional velocity-dependent terms) to allow immediate assessment of the derivation.

Simulated Author's Rebuttal

1 responses · 1 unresolved

We thank the referee for their careful review and the detailed comment on the symmetry aspects of the derivation. We address the major comment below.

read point-by-point responses

Referee: [Abstract and governing equations derivation] Abstract and main derivation: the claim that hand force without direct yaw torque can produce net frictional yaw torque via pressure redistribution is load-bearing but appears internally inconsistent with symmetry. A centered force Fx produces moment about the transverse axis and N(x) variation, but preserves N(x,y)=N(x,-y); thus τ_z = μ ∫ y N dA vanishes identically. Any lateral offset that breaks y-symmetry simultaneously supplies direct yaw torque via r × F. The derivation must explicitly show how the claimed mechanism evades this without reducing to direct torque or fitted parameters.

Authors: The referee correctly identifies that a centered horizontal force produces an N(x) redistribution that remains symmetric in y, so that the integral yielding τ_z vanishes. Any y-offset sufficient to break this symmetry simultaneously generates a direct yaw torque component via r × F. The manuscript derivation does not contain an explicit demonstration that the pressure-redistribution mechanism can produce net frictional yaw torque while evading both direct torque and additional fitted parameters. We are therefore unable to supply the requested resolution from the existing analysis. revision: no

standing simulated objections not resolved

Symmetry constraint on net frictional yaw torque without direct torque from force offset

Circularity Check

0 steps flagged

No circularity; no derivation chain or self-referential steps present to inspect

full rationale

The manuscript abstract asserts a formal derivation of governing equations for frictional torque arising from hand-force-induced pressure redistribution, yet supplies no equations, parameters, or citations at all. Without any load-bearing mathematical steps, fitted inputs, self-citations, or ansatzes to examine, none of the enumerated circularity patterns can be exhibited by direct quotation and reduction. The central claim therefore remains an unelaborated physical assertion rather than a constructed derivation, yielding a self-contained (if unverified) presentation.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Only abstract available; no explicit free parameters, axioms, or invented entities are stated. Standard Coulomb friction and rigid-body assumptions are implicitly required but not enumerated.

pith-pipeline@v0.9.1-grok · 5596 in / 926 out tokens · 30768 ms · 2026-06-27T02:34:36.250331+00:00 · methodology

0 comments

read the original abstract

When a wine glass is dragged on a table along a circular path, a spontaneous rotation about its vertical axis can develop even if the applied hand force does not directly introduce a yaw torque. This document provides a structured formal derivation of the governing equations that are responsible for this behavior. The analysis shows that the mechanism responsible for this effect is the redistribution of pressure onto the table when applying the force with your hand. This causes an uneven frictional force distribution which exerts a torque on the glass, causing it to spin.

Figures

Figures reproduced from arXiv: 2606.20694 by Ruben Canora.

**Figure 1.** Figure 1: Mechanical Configuration of the System. (a) Side View: The hand force Fhand is applied at height zF, offset from the Center of Mass (CM) at height zCM. This vertical misalignment generates an overturning moment about the CM which is balanced by the moment about the CM produced by the redistributed normal reaction, MN. (b) Top-Down View: The glass follows a circular path of radius ρ around center O. The app… view at source ↗

**Figure 2.** Figure 2: Yaw torque from asymmetric friction. A nonuniform normal load around the contact ring produces unequal friction forces at opposite points, breaking symmetry and generating a net yaw moment τz about the CM. The moment of an elemental friction force about the CM is dMf(θ) = rc(θ)×dFf(θ). The yaw torque is the vertical component of the total friction moment: τz = Z 2π 0 rc(θ)×dFf(θ) ·k. (35) As shown in … view at source ↗

**Figure 3.** Figure 3: Dynamics of the Finite Rotation Regime. (a) Numerical evaluation of the yaw torque τz as a function of angular velocity ω. The zero-crossing point identifies the terminal steady-state velocity (approximately −3.1 rad/s in this configuration). (b) The resulting time evolution of the angular velocity. Starting from rest, the glass accelerates in the negative direction, asymptotically approaching the terminal… view at source ↗

discussion (0)

Reference graph

Works this paper leans on

6 extracted references · 2 canonical work pages

[1]

F. P. Bowden and D. Tabor, The Friction and Lubrication of Solids (Clarendon Press, Oxford, 1950)

1950
[2]

K. L. Johnson, Contact Mechanics (Cambridge University Press, Cambridge, 1985)

1985
[3]

B. N. J. Persson, Sliding Friction: Physical Principles and Applications (Springer, Berlin, 2000)

2000
[4]

J. A. Greenwood and J. B. P. Williamson, ``Contact of nominally flat surfaces,'' Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences 295, 300--319 (1966). doi:10.1098/rspa.1966.0242

work page doi:10.1098/rspa.1966.0242 1966
[5]

H. K. Moffatt, ``Euler's disk and its finite-time singularity,'' Nature 404, 833--834 (2000). doi:10.1038/35009017

work page doi:10.1038/35009017 2000
[6]

Goldstein, C

H. Goldstein, C. P. Poole and J. L. Safko, Classical Mechanics, 3rd ed. (Addison-Wesley, San Francisco, 2002)

2002

[1] [1]

F. P. Bowden and D. Tabor, The Friction and Lubrication of Solids (Clarendon Press, Oxford, 1950)

1950

[2] [2]

K. L. Johnson, Contact Mechanics (Cambridge University Press, Cambridge, 1985)

1985

[3] [3]

B. N. J. Persson, Sliding Friction: Physical Principles and Applications (Springer, Berlin, 2000)

2000

[4] [4]

J. A. Greenwood and J. B. P. Williamson, ``Contact of nominally flat surfaces,'' Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences 295, 300--319 (1966). doi:10.1098/rspa.1966.0242

work page doi:10.1098/rspa.1966.0242 1966

[5] [5]

H. K. Moffatt, ``Euler's disk and its finite-time singularity,'' Nature 404, 833--834 (2000). doi:10.1038/35009017

work page doi:10.1038/35009017 2000

[6] [6]

Goldstein, C

H. Goldstein, C. P. Poole and J. L. Safko, Classical Mechanics, 3rd ed. (Addison-Wesley, San Francisco, 2002)

2002