Download 7TH CLASSES PHYSICS DAILY PLAN

9TH CLASSES
PHYSICS
DAILY PLAN
SUBJECT: TORQUE AND EQUILIBRIUM
GOALS:
DURATION:
IN PRACTICE:
If there are two or more forces acting on an object, then each has
a tendency to produce a rotation about the pivot at O and ;
NET = 1 + 2 + 3 +…..
Ex: According to given fig. compare the torques of F 1, F2 and F3
.
F1=10N
PRESENTATION:


0,5m
The term equilibrium implies either that the object is at rest
or that its centre of mass moves with constant velocity. We
deal here only with the former, which are referred to as
objects in static equilibrium.
0,5m
F3=20N
0,5m
O
370
F2=20N
STATIC EQUILIBRIUM
Static equilibrium represents a common situation in
engineering practice, and the principles involved are of
special interest to civil engineers, architects, and
mechanical engineers.
In order for an object to be in static equilibrium, the net force on
it must be zero and the object must have no tendency to rotate.
Therefore there exist two cases for static equilibrium and they
must be satisfied.
When a force is exerted on an object pivoted about some axis,
the body will tend to rotate about that axis.
1.

FNET=0  FxNET=0 & FyNET=0 (translational equilibrium)
The tendency of a force to rotate a body about some axis is
measured by a quantity called the torque and symbolized by
 (Greek letter tau).
F
According to rotational axis of an object the net torque
acting on the object must be zero.
NET = 0 ( rotational equilibrium )
l
O

2.
The resultant force acting on that body must be zero.
F1
NOTE:
Torque about a point O is the product of the force and the
perpendicular distance of its line of action from the point O.

 = F. l

Torque is a vector quantity. The direction of a torque is
along the axis of rotation and it is found by the right - hand
rule.
FORCE ( F )
N


F2
If the resultant force of the given three forces is zero:
TORQUE (  )
N.m
DISTANCE ( l )
m
F3


F1/sin =F2/sin=F3/sin

If  <  <   F3 > F2 > F1
Let  be the angle between F and l ;
This is known as Lami Theorem.
F
y
l
O

F
Ex: According to given figure find the magnitudes of tension ( T
) in the string and force ( F ).

F
x
370
T
d
=F.d
d = l sin
 = Fy.l
Fy = Fsin
F
W=10N
 = F.l.sin
Ex:
530
T1
 = F.l.sin
P=10N
370
T2
HOMEWORK:
MULTIMEDIA:
DEMONSTRATION:
EXPERIMENT:
TEACHER:
DIRECTOR: