May 2019 Issue,
Volume 87, No. 5
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
Editorial
AJP Reviewers by Richard H. Price. DOI: 10.1119/1.5096895
Papers
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
BOOKS RECEIVED
American Journal of Physics 87, 408 (2019); https://doi.org/10.1119/1.5096255. DOI: 10.1119/1.5096255
About AJP
General Information, Resources for Authors, Reviewers, and Readers