This is the story of a navigator and his spaceship.  Every protagonist has a goal; in this case, the navigator wants to travel through space.  Every protagonist must overcome some obstacles; this one must overcome Newton’s laws of motion.

1. Bodies at rest remain at rest and bodies in motion remain in motion unless some force acts on them (thrust, friction, gravity, etc…).  So in order for our navigator to begin his journey, he must get some force to act on his ship.  Since space is a frictionless vacuum, once the ship is moving it will not stop.
2. Forces must operate in straight lines, but multiple forces can combine through vector mathematics, allowing objects to travel in curves.  So if our navigator needs to follow anything other than a linear course, he’ll have to use more than one force to do it.
3. Every action has an equal and opposite reaction.  This law allows the spaceship to exert force on itself.  It simply launches some kind of propellant in one direction, and it will travel in the opposite direction.

Newton’s laws are simple enough, but taking advantage of them is an art form.  Piloting a spaceship, making it turn and twist around the stars, requires complex mathematical skills.  For the best pilots, vector calculations will become instinctive.

As our navigator flies through space, perhaps using Jupiter’s gravity to help change course, he still has one problem: how to stop.  Objects in motion stay in motion.  Hopefully, he saved enough fuel to counteract his enormous momentum.

Sources

“Newton’s Laws of Dynamics.” Van Nostrand’s Scientific Encyclopedia Eighth Edition.  Ed. Douglas M. Considine.  NY: Van Nostrand Reinhold, 1995.  Page 2172.

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