May 2019 AJP CoverMay 2019 Issue,

Volume 87, No. 5


A Candle Seesaw

A candle skewered transversely near its center of mass by a needle and balanced between two low-friction supports, when lit on both ends, will drip asymmetrically and begin to oscillate like a seesaw; these oscillations grow in time. We examine the onset of instability, and find that the candle does not oscillate quasi-stably until the vertical center of mass is lowered by the symmetrical melting of each end, creating a physical pendulum with a well-defined characteristic period. Additional asymmetric dripping below horizontal drives the pendulum, leading to linear growth in amplitude. The drop release becomes phase locked to the seesaw motion of the candle. We develop a small-angle analytical model that predicts the maximum growth rate when the dripping rate matches the seesaw frequency. Measurements of the motion, droplet phase, and melting rate confirm the validity of the model. We compare our results to earlier studies and make suggestions for the demonstrator.


Letter to the Editor

Quantum no-cloning theorem and entanglement by Mark G. Kuzyk. DOI: 10.1119/1.5093815

Guest Editorial

Have a passion for teaching? Consider high school teaching by W. K. Adams, M. Plisch, and T. Plantt. DOI: 10.1119/1.5094433


AJP Reviewers by Richard H. Price. DOI: 10.1119/1.5096895


Resource Letter RBAI-2: Research-based assessment instruments: Beyond physics topics by Adrian Madsen, Sarah B. McKagan, Eleanor C. Sayre, and Cassandra A. Paul. DOI: 10.1119/1.5094139

The candle seesaw by Paul J. H. Tjossem, William B. Case, and Rachel M. Bass. DOI: 10.1119/1.5096886

Rousing the dragon: Polonium production for neutron generators in the Manhattan Project by B. Cameron Reed. DOI: 10.1119/1.5094138

Peculiarities in the gravitational field of a filamentary ring by Dániel Schumayer, and David A. W. Hutchinson. DOI: 10.1119/1.5092450

How bright was the Big Bang? by Christopher Andersen, Charlotte Amalie Rosenstroem, and Oleg Ruchayskiy. DOI: 10.1119/1.5092705

Back of the Envelope

Fleeing from the quadratic formula by Sanjoy Mahajan. DOI: 10.1119/1.5097757

Physics Education Research

New video resource for calculus-based introductory physics, design and assessment. I. Electricity and magnetism by Jonathan D. Perry, Tatiana L. Erukhimova, and William H. Bassichis. DOI: 10.1119/1.5095140

Computational Physics

Polarization in electrostatics and circuits: Computing and visualizing surface charge distributions by Ruth Chabay, and Bruce Sherwood. DOI: 10.1119/1.5095939

Notes and Discussions

Reply to ‘Comment on “ ‘Relativistic’ particle dynamics without relativity” ’ [Am. J. Phys. 87, 144–145 (2019)] by Allan Walstad. DOI: 10.1119/1.5095944

Comment on “Acceleration due to buoyancy and mass renormalization” [Am. J. Phys. 87, 165–170 (2019)] by David Derbes, David Griffiths, and Richard Sohn. DOI: 10.1119/1.5096256

Comment on “Relativistic phase velocity transformation” [Am. J. Phys. 57(7), 628–630 (1989)] by Samuel Picton Drake, and Geoff Pointer. DOI: 10.1119/1.5096624

Book Reviews

A Student's Guide to General Relativity by Neil F. Comins. DOI: 10.1119/1.5094771

It Keeps Me Seeking: An Invitation from Science, Philosophy, and Religion by Milan M. Cirkovic. DOI: 10.1119/1.5090484


American Journal of Physics 87, 408 (2019); DOI: 10.1119/1.5096255

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