Determine the SI base units that correspond to the moment of a force.
A uniform square card ABCD is pinned freely at a point P by a pin. It is kept in a vertical plane by an external force in the arrangement shown in Fig. 1.1. The card weighs $0.15\,\text{N}$ and this may be treated as acting at its centre of gravity $G$. Each edge of the card is $17\,\text{cm}$ long. Point P lies on the horizontal line AC and is $4.0\,\text{cm}$ from corner A. Line BD is vertical. The external force is removed and the card is released. It then swings in a vertical plane until it comes to rest.
Calculate the size of the resultant moment about point P on the card immediately after it is released.
Explain why the card’s centre of gravity is vertically below point P after it has come to rest.