Chapt. 5
Newton’s Laws and Dynamics I
49
005 qmult 00534 1 5 1 easy memory: Newton’s 2nd law class mantra 1
13. From here on in this course, a key thing to remember (to recite to yourself) when faced with
any force problem is that Newton’s 2nd law (
vector
F
net
=
mvectora
) is:
a)
ALWAYS VALID
. And it is a
VECTOR
equation, and so is always
VALID
component
by component. And
vector
F
net
is the
VECTOR
sum of all forces acting on the body of mass
m
.
It is not any particular force. If all the forces sum to zero vectorially,
vector
F
net
=
mvectora
= 0. If
you are given the acceleration, then you can often use
vector
F
net
=
mvectora
to solve for an unknown
force.
b)
ALWAYS VALID
. And it is a
SCALAR
equation. And
vector
F
net
is the
SCALAR
sum of
all forces acting on the body of mass
m
.
It is not any particular force.
If all the forces
sum to zero,
vector
F
net
=
mvectora
= 0.
If you are given the acceleration, then you can often use
vector
F
net
=
mvectora
to solve for an unknown force.
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 Fall '06
 Buchler
 Physics, Force, Fnet

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