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Question
If Newton's law of motion, which states that any object in motion will remain in motion, is true, then why is it that as a comet gets close to the sun and it melts, and a tail forms, and why wouldn't it be just a big ball of melted stuff?
Asked by: Nakul Jeirath
Answer
Newton's First Law of Motion actually states that a body in motion will remain in motion
UNLESS ACTED UPON BY AN OUTSIDE FORCE. In the case of a comet, there are a number of
outside forces acting upon it.
The primary force on a comet, of course, is gravitational as it orbits the Sun. That force,
however, acts more or less uniformly on all parts of the comet (ignoring tidal forces).
Other forces, however, include the Solar Wind (a stream of subatomic particles emitted by
the Sun) and sunlight itself. While these forces are small and have little effect on the
large mass of the comet, they are large enough to influence the smaller mass of its tenuous
tail. The small particles of dust and gas that form as the comet's material is heated near
the sun are 'blown' outward, away from the sun and the comet's main body, because their
small mass is more easily accelerated by the small forces mentioned above.
Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor
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