Question

The pressure at the bottom of a swimming pool is evenly distributed. Suppose we look at a cast iron plate of 7272 kg lying on the ground with an area of 100 m². What is the average pressure below that? Is it just as evenly distributed? 

Answer 1

The pressure is force per unit area 

P = F/A = mg/A = 7272 kg × (9.81 m/s²) / 100 m² = 713.4 Pa

The iron plate being cast can be reasonable plane and flat, but it is stiff and rigid. However, the ground is usually uneven so the contact between the plate and the ground is made over an area much smaller than the 100 m². Thus the local pressure at the contact locations is much larger than the quoted value above.

The pressure at the bottom of the swimming pool is very even due to the ability of the fluid (water) to have full contact with the bottom by deforming itself. This is the main difference between a fluid behavior and a solid behavior.

   Iron plate Ground