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FORCE:

The product of mass multiplied by acceleration.

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FRICTION:

The force that resists motion when the surface of one object comes
into contact with the surface of another.

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INERTIA:

The tendency of an object in motion to remain in motion, and of an
object at rest to remain at rest.

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INVERSE RELATIONSHIP:

A situation involving two variables, in which one of the two increases
in direct proportion to the decrease in the other.

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LAW OF UNIVERSAL GRAVITATION:

A principle, put forth by Sir Isaac Newton (1642-1727), which states
that every object in the universe attracts every other one with a
force proportional to the masses of each, and inversely proportional
to the square of the distance between them.

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MASS:

A measure of inertia, indicating the resistance of an object to a
change in itsmotion.

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TERMINAL VELOCITY:

A term describing the rate of fall for an object experiencing the drag
force of air resistance. In a vacuum, the object would continue to
accelerate with the force of gravity, but in most real-world
situations, air resistance creates a powerful drag force that causes a
leveling in the object's rate off all.

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VACUUM:

Space entirely devoid of matter, including air.

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WEIGHT:

A measure of the gravitational force on an object; the product of mass
multiplied by the acceleration due to gravity.