Turning effects of forces

Moment

• The moment of a force is the product of the force and the perpendicular distance from the pivot to the line of action

• M = f/d

Principle of momemnts

When a body is in equilibrium:

• sum of clockwise moment about the pivot is equal to the sum of anti-clockwise moments about the same pivot

• upward force = downward force

Centre of gravity

The centre of gravity is defined as the point on ht object where its whole weight seem to be acting on

Stability

• The stability of an object is a measure of its ability to return to its original position after being slightly displaced

• Stability of the objects can be increased by keeping the centre of gravity as low as possible and keeping the base area as wide as possible

• Stable: cone on its base, line of action through its weight still lies within its base after tilting. The moment of weight aboutits contact point returns the cone to its original position

• Unstable: Cone on its tip, Line of action through its weight lies outside its base after tilting. The moment of weight about its contact point causes the cone to be toppled

• Neutral: Cone is lying horizontally on the floor. Line of action through its weight and its contact force coincide. The moment about the contact point is 0, it stays in the position it is displaced