Moment of a Force, Definition of Torque, Second Condition of Equilibrium, Solving Problems using First and Second Laws of Motion

1. MOMENT OF A
FORCE

2. Objectives
 To analyze non- concurrent forces acting on
an object.
 To verify the second condition of equilibrium.
 To analyze forces using 1st and 2nd condition of
equilibrium.

3. Moment o f a Fo r c e , M o r T
me a s u r e o f t h e a b i l i t y o f a f o r c e
t o p r o d u c e r o t a t i o n a b o u t a n a x i s
T = f o r c e x mome n t a r m
= F d
* Mome n t a rm i s t h e p e r p e n d i c u l a r
d i s t a n c e o f t h e l i n e o f a c t i o n o f
t h e f o r c e f r om t h e a x i s o f r o t a t i o n
e x . s e e s a w

4. Un i t o f Mome n t i s
Nm (MK S )
d y n e cm ( C G S )
l b f t ( E n g l i s h )

5. F1
F1, F2, and F3 are
non-concurrent
forces.
F2 F3

7. Second Condition of Equilibrium
 Equilibrium of Non – concurrent Forces
 The sum of all the torques acting on an
object is zero.
ΣT = 0

8. Exercises
1. A uniform 30-lb beam 10 feet long is
carried by two men A and B, one at each of
the beam. If A exerts a force of 25 lb, where
must a load of 50 lb be placed on the
beam? What force does B exert?

9. 2. A weight W1 balances a 5.0 lb weight, W2,
on the other side of the fulcrum. Calculate
the value of W1 and the force exerted by the
fulcrum?
10 in 13 in
W2
W1

10. 3. A meter stick is free to rotate about its
center. A load of 85 grams is hung at the
100 cm mark. What load should be placed
at the 30 cm mark so that the meter stick
will remain in a horizontal position?