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Newton's First Law of Motion - Inertia

Vocabulary words and important facts from Chapter 3: Newton's First Law of Motion - Inertia from the Prentice Hall Conceptual Physics textbook. Big Idea: force causes change in motion.
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friction
the force that acts between materials as they move past each other
inertia
the property of a body to resist changes to its state of motion
When is a force needed to keep an object in motion?
A force is needed to keep an object in motion when friction is present.
Newton's first law (the law of inertia)
Newton's first law states that every object continues in a state of rest, or in a uniform speed in a straight line, unless acted on by a nonzero net force.
mass
the quantity of matter in an object
mass is measured in...
kilograms
weight
the force of gravity on an object
What is the relationship between mass and inertia?
The more mass an object has, the greater its inertia and the more force it takes to change its state of motion.
How does the law of inertia apply to objects in motion?
The law of inertia states that objects in motion stay in motion if no unbalanced forces act on them.