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Chapter 4 Forces and Newton’s Laws of Motion
47
Chapter 4
FORCES AND NEWTON’S LAWS OF MOTION
PREVIEW
Dynamics
is the study of the
causes
of motion, in particular,
forces
. A force is a push or a
pull. We arrange our knowledge of forces into three laws formulated by Isaac Newton:
the law of inertia, the law of force and acceleration
(
F
net
= m
a
), and
the law of action
and reaction. Friction
is the force applied by two surfaces parallel to each other, and the
normal force
is the force applied by two surfaces perpendicular to each other.
Newton’s
law of universal gravitation
states that all masses attract each other with a gravitational
force which is proportional to the product of the masses and inversely proportional to the
square of the distance between them. The gravitational force holds
satellites
in orbit
around a planet or star.
The content contained in all sections of chapter 4 of the textbook is included on the AP
Physics B exam.
QUICK REFERENCE
Important Terms
coefficient of friction
the ratio of the frictional force acting on an object to the normal force exerted by
the surface in which the object is in contact; can be static or kinetic
dynamics
the study of the causes of motion (forces)
equilibrium
the condition in which there is no unbalanced force acting on a system, that is, the
vector sum of the forces acting on the system is zero.
force
any influence that tends to accelerate an object; a push or a pull
free body diagram
a vector diagram that represents all of the forces acting on an object
friction
the force that acts to resist the relative motion between two rough surfaces which
are in contact with each other
gravitational field
space around a mass in which another mass will experience a force
gravitational force
the force of attraction between two objects due to their masses
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48
inertia
the property of an object which causes it to remain in its state of rest or motion at
a constant velocity; mass is a measure of inertia
inertial reference frame
a reference frame which is at rest or moving with a constant velocity; Newton’s
laws are valid within any inertial reference frame
kinetic friction
the frictional force acting between two surfaces which are in contact and moving
relative to each other
law of universal gravitation
the gravitational force between two masses is proportional to the product of the
masses and inversely proportional to the square of the distance between them.
mass
a measure of the amount of substance in an object and thus its inertia; the ratio of
the net force acting on an accelerating object to its acceleration
net force
the vector sum of the forces acting on an object
newton
the SI unit for force equal to the force needed to accelerate one kilogram of mass
by one meter per second squared
noninertial reference frame
a reference frame which is accelerating; Newton’s laws are not valid within a
noninertial reference frame.
normal force
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This note was uploaded on 03/30/2012 for the course PHYSICS 201 taught by Professor Rollino during the Fall '11 term at Rutgers.
 Fall '11
 rollino
 Physics, Force, Second Law Of Motion

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