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THE INERTIA OF LIGHT. VERIFICATION OF NEWTON’S SECOND LAW BY A CONFINED FLOW OF RADIATION IN A REFLECTIVE CAVITY

Authors

C.M. Figueroa Laboratorio de Física del Sólido, INFINOA (CONICET-UNT), Facultad de Ciencias Exactas y Tecnología, Universidad Nacional de Tucumán, 4000 San Miguel de Tucumán, Argentina
S. Saracho Departamento de Física-FACET– Universidad Nacional de Tucumán. Av. Independencia 1800 – (4000) Tucumán – Argentina

Abstract

In 1904, the Austrian physicist Fritz Hasenöhrl examined by means of mental experiments the black body radiation in
a reflecting cavity. By calculating the work required to keep the cavity moving at constant velocity in opposition to the
radiation pressure, he calculated for the radiation energy a value equivalent to E =3/8mc², relation corrected in 1905 to
E =3/4mc². This relation establishes an equivalence between mass m and radiation energy E and was finally corrected to
the present known form E = mc² by Einstein. The conclusion from these deductions is that light has mass and inertia.
Based on a thought experiment inspired by Hasenöhrl’s, in which we accelerate a reflecting cavity containing an internal
radiation flux, we conclude that, under certain conditions of motion, light verifies Newton’s 2nd Law of Inertia.