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Concept: Pendulum clock


The synchronization of two pendulum clocks hanging from a wall was first observed by Huygens during the XVII century. This type of synchronization is observed in other areas, and is fundamentally different from the problem of two clocks hanging from a moveable base. We present a model explaining the phase opposition synchronization of two pendulum clocks in those conditions. The predicted behaviour is observed experimentally, validating the model.

Concepts: Scientific method, Hypothesis, Das Model, Base, Problem of evil, Pendulum clock, Christiaan Huygens


This paper introduces a modern version of the classical Huygens' experiment on synchronization of pendulum clocks. The version presented here consists of two monumental pendulum clocks-ad hoc designed and fabricated-which are coupled through a wooden structure. It is demonstrated that the coupled clocks exhibit ‘sympathetic’ motion, i.e. the pendula of the clocks oscillate in consonance and in the same direction. Interestingly, when the clocks are synchronized, the common oscillation frequency decreases, i.e. the clocks become slow and inaccurate. In order to rigorously explain these findings, a mathematical model for the coupled clocks is obtained by using well-established physical and mechanical laws and likewise, a theoretical analysis is conducted. Ultimately, the sympathy of two monumental pendulum clocks, interacting via a flexible coupling structure, is experimentally, numerically, and analytically demonstrated.

Concepts: Scientific method, Science, Theory, Harmonic oscillator, Simple harmonic motion, Pendulum clock, Christiaan Huygens, Escapement


This editorial article initiates the school scoliosis screening thematic series of the Scoliosis journal. The various issues on screening policies are discussed; clinical and practical recommendations of setting up school screening programs are also described.

Concepts: Scoliosis, The Various, Pendulum, Pendulum clock


Evidence is building to support consideration of anterolateral knee reconstruction in the anterior cruciate ligament-deficient knee with a high-grade pivot shift or participation in a high-risk sport. As the pendulum swings back to the future with the extra-articular augmentation, our anticipation should be tempered by cautious interpretation of the results as the controversy unfolds.

Concepts: Future, Knee, Anterior cruciate ligament, Anterior cruciate ligament reconstruction, Cruciate ligament, Pendulum, Pendulum clock


Synchronization of coupled oscillators has been scrutinized for over three centuries, from Huygens' pendulum clocks to physiological rhythms. One such synchronization phenomenon, dynamic mode locking, occurs when naturally oscillating processes are driven by an externally imposed modulation. Typically only averaged or integrated properties are accessible, leaving underlying mechanisms unseen. Here, we visualize the microscopic dynamics underlying mode locking in a colloidal model system, by using particle trajectories to produce phase portraits. Furthermore, we use this approach to examine the enhancement of mode locking in a flexible chain of magnetically coupled particles, which we ascribe to breathing modes caused by mode-locked density waves. Finally, we demonstrate that an emergent density wave in a static colloidal chain mode locks as a quasi-particle, with microscopic dynamics analogous to those seen for a single particle. Our results indicate that understanding the intricate link between emergent behaviour and microscopic dynamics is key to controlling synchronization.

Concepts: Condensed matter physics, Liquid, Oscillation, Wave, Phase, Periodic function, Simple harmonic motion, Pendulum clock


Christiaan Huygens (1629-1695) was a Dutch mathematician, physicist, and astronomer. He became well-known as inventor of the pendulum clock and described light as a wave phenomenon. He became Fellow of the Royal Society (London) and member of the Académie des Sciences (Paris). From the correspondence with family members and famous scientists, we learn that he suffered from frequent headaches.

Concepts: Netherlands, Scientist, Robert Hooke, Pendulum, Horology, Pendulum clock, Christiaan Huygens