•A Force applied to a body can cause a turning effect about a fixed point called the pivot point.
•Moment of a force (torque) = product of force and perpendicular distance from the pivot to the line of action of the force.
•It is a measure of the turning effect of a fore .
•SI unit is (Nm) Newton meter.
•The moment of a force is a vectos quantity. It has two possible directions: clockwise or anticlockwise.
•The principle of moments states that when body is in equilibrium, the sum of clockwise moment about a pivot is equal to the sum of anticlockwise moments about the same pivot.
•For a startionary object, the forces acting on it are balanced i.e the resultant force is zero.
- Similary from moment when a object does not rotate, the clockwise and anticlockwise moment acting on it are balanced i.e the resultant moment is zero.
The object in equilibrium must satisfy following conditions:
•The resultant force on object is zero.
•The resultant moment on object is zero.
•The center of gravity of any object is defined as the point through which its whole weight of the body acts.
•For any object of regular shape and uniform density, the center of gravity is at its geometrical center.
•The center of gravity is usually located near the region that has more mass.
•The stability of an object is a measure of its ability to return to its original position after it is slightly displaced.
•Stable equilibrium is when center of gravity rises before it returns to its original position. The line of action through its weight still lies within its base. The moment of the weight cause it to return to its original position.
• Unstable equilibrium is when its center of gravity is dropped. The line of action through its weight lies outside its base. The moment of weight cause it to topple.
• Neutral equilibrium is when center of gravity remain at same height when it is slightly displaced. The line of action through its weight and contact force R conincides. The moment of weight is zero.
• To increase stability center of gravity must be as low as possible.
• Base ares should as wide as possible.
• To find center of mass of a irregular shape:
•Hang the card from pin.
•Suspend lamina next to the plumb line.
•Mark vertical line on lamina.
•Repeat from another point and point of intersection is the center of mass.
• The center of mass is a place where whole mass seems to be located.
• Center of mass is a region where object balances.
