MasteringPhysics: Assignment Print View
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10/4/2007 3:42 PM
PHCC 141: Physics for Scientists and Engineers I - Fall 2007
4a. Newton's Laws and Examples
Due at 11:59pm on Friday, September 14, 2007
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Newton's First Two Laws
Newton's 1st Law
To understand Newton's 1st law.
states this first law of motion:
An object subject to no net force maintains its state of motion, either at rest or at constant speed in a right line.
This law may be stated as follows: If the sum of all forces acting on an object is zero, then the acceleration of that object is zero.
Mathematically this is just a special case of the 2nd law of motion,
, prompting scholars to advance the
following reasons (among others) for Newton's spelling it out separately:
This expression only holds in an inertial coordinate system--one that is not accelerating--and this law really says you have to
use this type of coordinate system (i.e., Newton's laws won't work inside an accelerating rocket ship.)
This was a direct challenge to the Impetus theory of motion, described as follows:
A mover, while moving a body, impresses on it a certain impetus, a certain power capable of moving this body in
the direction in which the mover set it going, whether upwards, downwards, sideways or in a circle. By the same
amount that the mover moves the same body swiftly, by that amount is the impetus that is impressed on it powerful.
It is by this impetus that the stone is moved after the thrower ceases to move it; but because of the resistance of the
air and the gravity of the stone, which inclines it to move in a direction opposite to that towards which the impetus
tends to move it, this impetus is continually weakened. Therefore the movement of the stone will become
continually slower, and at length, the impetus is so diminished or destroyed that the gravity of the stone prevails
over it and moves the stone down towards its natural place.
A. C. Crombie,