Physics XI Content
TORQUE CENTRE OF GRAVITY
TORQUE CENTRE OF GRAVITY




DEFINITION


“ The tendency of a force to produce rotation in a body
about an axis is called torque or momentum of force.“ 

MATHEMATICAL DEFINITION


Torque produced in a body is numerically equal to the product of force and moment arm.


Torque = (force ) ( moment arm)


VECTORIAL DEFINITION


Torque produced in a body is equal to the cross product of
force arm ( ) and the force ( ). 

The turning effect of a force depends upon two factors:
The torque about any axis is given by the product of force and moment arm. 

EXPLANATION


Consider a particle of mass ‘m’ which is acted upon a force. Let be the position vector of the particle which is also the position vector of the point of application of force. We can resolve this force into two rectangular components: 1. Parallel to the position vector i.e. Or Fcosq 2. Perpendicular to the position vector i.e. Or Fsinq 

From figure, it is clear that can pull the particle but it cannot rotate it or it is unable to produce torque in the mass. It is the component which produces rotation in the mass. Let r and be the magnitude of and respectively. The magnitude of the torque produced about the centre ‘O‘ is defined as: 

Where q is the smaller angle between the positive direction of and .  
Using vector notation, above expression can also be written as :  
DIRECTION OF TORQUE


The direction of torque is directed along the normal to the plane formed by and as given by righthand rule.  
SIGN CONVENTION


Positive torque: If a body rotates about its axis in anticlockwise direction, then the torque is taken positive. 

Negative torque: If the body rotates in the clockwise direction, then the torque is taken as negative. 

DETERMINANT FORM OF TORQUE


Let the position vector is = x i+ y j+ z k and the force= F_{x} i+ F_{y} j+ F_{z }k  
The torque is given by:  
UNIT OF TORQUE


In SI system unit of torque is Nm ( Newton . Metre)  
DIMENSION OF TORQUE


[L^{2}MT^{2}]


