In I/GCSE Physics, forces have a **turning effect**. They tend to make objects turn around a fixed point called **a** **pivot **or** a fulcrum**. The turning effect of a force about a pivot is called its **moment**.

*Moment (Nm) = force (N) x perpendicular distance from pivot (m)*

The perpendicular distance is basically the distance from the pivot to the line of force. It has to be **90 ^{0}** for the correct value.

An object will be in **balance** if: **Sum of anticlockwise moments = sum of clockwise movements**

Centre of Gravity

The centre of gravity is the point where **the whole of the weight of the object appears of act**.

It can be found by drawing lines of **symmetry **(if the object is rectangular or symmetrical) and finding the point which all the lines intersect, or, for an irregular shape, by suspending it freely by a point on its edge and using a **plumb line **to indicate **the space directly vertical to the point** in the I/GCSE physics.

The centre of gravity is always **vertically below the pivot** so you can work out the centre of gravity by drawing a point somewhere in the **middle of the plumb line**, or **suspending the object** at different points on its edge and finding out where all the lines **intersect**.

In I/GCSE physics curriculum, objects with a **low centre of gravity** and a **wide base** are **stable** as it is difficult to knock over.

End of part I, remember to read part II !