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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