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Comets move around the sun in highly elliptical orbits. The gravitational force on the comet due to the sun is not normal to the comet's velocity in general. Yet the work done by the gravitational force over every complete orbit of the comet is zero. Why?

The gravitational force of the Sun does positive work when the comet moves from apogee to perigee and the gravitational force of the Sun does same amount of negative work when it goes from perigee to apogee.

Hence net work done by the gravitational force of the Sun on the comet in one complete cycle is zero.

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Comets move around the sun in highly elliptical orbits. The gravitational force on the comet due to the sun is not normal to the comet's velocity in general. Yet the work done by the gravitational force over every complete orbit of the comet is zero. Why?

Work, Energy and Power

Comets move around the sun in highly elliptical orbits. The gravitational force on the comet due to the sun is not normal to the comet's velocity in general. Yet the work done by the gravitational force over every complete orbit of the comet is zero. Why?