**Centre of Pressure**

When a body is immersed in a liquid, it experiences a force called buoyant force. The buoyant force is equal to the weight of the liquid displaced by the body and it acts vertically upward. This force gives rise to a pressure distribution on the surface of the immersed body.

The resultant pressure of the liquid in case of an immersed body acts through the centre of pressure. The centre of pressure is the point at which the total pressure force on the body acts. It is the point of application of the resultant pressure force. The position of the centre of pressure depends on the shape and orientation of the immersed body.

**Explanation:**

To understand why the resultant pressure acts through the centre of pressure, let's consider an example of a submerged rectangular plate.

When a rectangular plate is immersed in a liquid, the pressure on the upper surface of the plate is greater than the pressure on the lower surface. This is because the pressure increases with depth in a fluid. The pressure difference creates a net force that acts on the plate. This net force is equal to the product of the pressure difference and the area of the plate.

The net force acts at a certain point on the plate, known as the centre of pressure. The position of the centre of pressure depends on the shape and orientation of the plate. For a rectangular plate, the centre of pressure lies along the vertical line passing through the centroid of the plate.

In general, the centre of pressure is the point where the sum of the moments of pressure forces about any axis is zero. It is a point that represents the average position of the pressure forces acting on the immersed body.

Therefore, the resultant pressure of the liquid in case of an immersed body acts through the centre of pressure. This is the point where the total pressure force on the body is considered to be applied.