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Summary
Selected Vocabulary
weight...............................the force of gravity on an object, equal to mg
inertial frame.....................a frame of reference that is not accelerating, one in which Newton’s first
law is true
noninertial frame...............an accelerating frame of reference, in which Newton’s first law is violated
Terminology Used in Some Other Books
net force............................another way of saying “total force”
Notation
F
W.....................................................
the weight force
Summary
Newton’s first law of motion states that if all the forces on an object cancel each other out, then the object
continues in the same state of motion. This is essentially a more refined version of Galileo’s principle of
inertia, which did not refer to a numerical scale of force.
Newton’s second law of motion allows the prediction of an object’s acceleration given its mass and the
total force on it, a=F
total
/m. This is only the one-dimensional version of the law; the full-three dimensional
treatment will come in chapter 8, Vectors. Without the vector techniques, we can still say that the situation
remains unchanged by including an additional set of vectors that cancel among themselves, even if they are
not in the direction of motion.
Newton’s laws of motion are only true in frames of reference that are not accelerating, known as inertial
frames.
Chapter 4Force and Motion
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