LAB # 13 Equilibrium of a Rigid Body
Introduction:
The two conditions for a rigid body to be in equilibrium are:
a. the resultant of all the forces acting on the body must equal zero:
F
i
=
0
!
(1)
b. the resultant of all the torque's acting on a body (computed around any axis) must
equal zero.
S
i
= 0
(2)
As discussed in your textbook, a torque may be identified with the ability of a force to
produce rotation. A torque depends on three factors:
a. the magnitude of the force.
b. the direction of the force.
c. the point of application of the force on a rigid body relative to some axis of rotation.
These factors may be combined in the equation:
!
=
F
(
L
sin
"
)
(3)
where:
τ
= torque
F
= force
L
= vector from the axis of rotation to the point application of the force.
θ
= angle between F and L
( see Fig. 1).
`
Thus the torque would take on its maximum value when
θ
= 90
°
so that sin
θ
= 1.
It is convenient to regard a torque which would produce rotation in a counterclockwise
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 Fall '08
 RABE
 Physics, Force, Mass, #, 90°, one quarter, 0.1 g

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