The Greek letter Tau
The Physical Study of Balance
Sum of forces is zero
Tendency to rotate is zero
the effectiveness of a force in causing rotation
on a rigid object
also called moment of force

Which of the following forces will
effectively rotate the beam at point O?

Which of the following forces will
effectively rotate the beam at point O?

Which of the following forces will
effectively rotate the beam at point O?

Which of the following forces will
effectively rotate the beam at point O?


The amount of force perpendicular to the lever arm.
The distance of the force from the pivot point.
Illustrate all the forces and the lever arm for
each.
 Torque is the product of force and its distance
from the point of rotation.
 Force and the lever arm must always be
perpendicular.
 Establish the point of rotation.
 Equate the sum of forces to zero.
 Equate the sum of torques to zero.

A 50.0 N uniform beam, 10.0 m in length, is suspended
on a support as shown. If the fulcrum divides the beam
into the ratio of 2:3, where should a 6.00 kg object be
placed to balance the beam?
x

In a Singkil dance, two men are carrying a princess on
a bamboo pole that is 5.00 m long and weighs 200.0
N. If the princess weighs 425 N and sits 1.50 m from
one end, how much weight must each man support?


(Follow up)
Where should the princess sit so that one man
supports her with a force twice that of the other?
?

Consult page
117 of your book
and read
Practice
Exercise 5.8
Rx
lRx
w
Ry
f
1m
lw
A uniform 50.0 N ladder
rests on a frictionless wall
as shown. What
minimum coefficient of
friction is needed on the
ground to prevent it from
slipping?
5m
2m
A uniform aluminum beam 9.00 m long, weighing 300 N,
rests symmetrically on two supports 5.00 m apart. A boy
weighing 600 N starts at point A and walks toward the
right.
 From your diagram, how far beyond point B can the boy
walk before the beam tips?