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Fore
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Torque


The torque or moment of force can be define as  
“
The tendency of a force to produce rotation in a body
about an axis is called torque or moment of force." 

The
turning effect of a force depends upon two factors: The magnitude of force (F) Moment arm (r) The torque about any axis is given by the product of force and moment arm 

Torque
= force x moment arm
OR 

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

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

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Center
of gravity


The center of a body is that point in the body through
which the resultant forces due to the earth’s attraction
posses and through which the whole weight of the body always acts. OR Center of gravity of a body is a point where total weight of the body is concentrated. Every body posses a center of gravity and this is irrespective of the body. Its is not necessary that the center of gravity should be within the body, but it may also be situated in space out side the body. Example: center of gravity of a ring is at the center, which is in the space. Center of gravity of different objects: Rectangle Center of gravity of a rectangular is at the point of intersection of its diagonals Circle Center of gravity of a circle is at its center.
Square The center of gravity of a regular bar is at its geometrical center. Triangle The center of gravity of a triangle is at the point of intersection of its medians. Cylinder The center of gravity of a cylinder is at the axis of cylinder. 

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