The Atwood machine revisited using smartphones

Abstract

The Atwood machine is a simple device used for centuries to demonstrate the Newton's second law.It consists of two supports containing different masses joined by a string. Here, we propose an experiment in which a smartphone is fixed to one support. With the aid of the built-in accelerometer of the smartphone the vertical acceleration is registered. By redistributing the masses of the supports, a linear relationship between the mass difference and the vertical acceleration is obtained.In this experiment, the use of a smartphone contributes to enhance a classical demonstration. TheoryThe Atwood machine is a simple device invented in 1784 by the English mathematician George Atwood [1][2][3] . It consists of two objects of mass m A and m B , connected by an inextensible massless string over an ideal massless pulley 1 . Applying the Newton's second law to each mass we obtainwhere g is the gravitational acceleration, T is the tension force, and a is the vertical acceleration.Eliminating the tension between these equations we obtainor in terms of the mass difference Δm and the total mass MAs mentioned in the original Atwood's book, many possible experiments can be implemented using his machine 1 . One of the simplest possibilities, adopted here, is, keeping the total mass, to vary Δ m by redistributing a set of weights. In this case, a linear relationship between the vertical acceleration and the mass difference is obtained.

The Effect of a Tangential Frictional Force on Rotating Disks: An Experimental Approach

“…The use of the video analysis allows the user to eschew sensors, interfaces, and dedicated software, and proves again to be a reliable tool in mechanics physics courses. [6][7][8][9][10][11][12][13] Acknowledgments CFisUC gratefully acknowledges funding from FCT Portugal through grant UID/FIS/04564/2016. P.M-R would like to thank Santander Universidades for its financial support through the "Becas Iberoamérica Jóvenes Profesores e Investigadores, España" scholarship program.…”

Smartphones y caída libre: Diseño y evaluación de una experiencia práctica

“…En la bibliografía reciente se pueden encontrar numerosas propuestas de experiencias prácticas de Física basadas en la utilización de smartphones y/o tablets como herramientas de medida en experiencias de mecánica (Kuhn y Vogt, 2012;Vogt y Kuhn, 2012a, 2012bCastro-Palacio, Velázquez-Abad, Giménez y Monsoriu, 2013;Vieyra y Vieyra, 2014;Hochberg, Gröber, Kuhn y Müller, 2014;Monteiro, Stari, Cabeza y Martí, 2015), acústica (Parolin y Pezzi, 2013;Kuhn y Vogt, 2013b;Kuhn, Vogt y Hirth, 2014;Parolin y Pezzi, 2015;González y González, 2016;Di Laccio Caceres et al, 2017) u óptica (Sitar, 2012;Thoms, Colicchia y Girwidz, 2013;Monteiro, Stari, Cabeza y Martí, 2017;Sans et al, 2017;Salinas, Giménez, Monsoriu y Castro-Palacio, 2018). Sin embargo, hasta ahora no se ha empezado a comprobar la eficacia de la utilización de smartphones y/o tablets como herramientas de medida en experiencias prácticas en el aprendizaje de la Física por parte del alumnado.…”

Dispositivo para medir tiempo y temperatura usando un microcontrolador

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