Gases and Liquids (fluids) exert pressure on surfaces because of the constant collisions of their molecules with the surfaces. The force exerted by a column of liquid on a surface is its weight.
Since density ρ = mass per unit volume the weight of the column is given by mass × g which equals (ρV) × g.
The volume V of the column is A×h where A is the cross-sectional area and h is the height of the column.
Therefore the pressure is given by force / Area
so P = ρ g h
If you push a piece of wood into water, you immediately feel a force pushing it upwards and the force pushes it out of the water. A buoyant force exists because of pressure differences between the top and lower surfaces of the wood.
The force at the top surface is equal to:
hρgA
The force at the bottom surface is equal to:
(h + x)ρgA
The difference between the forces at the top and bottom surfaces is
(h + x)ρgA - hρgA
The resultant force xρgA is called the upthrust and is equal to the weight of the fluid displaced by the block.
This is known as the Archimedes Principle.
Since density ρ = mass per unit volume the weight of the column is given by mass × g which equals (ρV) × g.
The volume V of the column is A×h where A is the cross-sectional area and h is the height of the column.
Therefore the pressure is given by force / Area
so P = ρ g h
If you push a piece of wood into water, you immediately feel a force pushing it upwards and the force pushes it out of the water. A buoyant force exists because of pressure differences between the top and lower surfaces of the wood.
The force at the top surface is equal to:
hρgA
The force at the bottom surface is equal to:
(h + x)ρgA
The difference between the forces at the top and bottom surfaces is
(h + x)ρgA - hρgA
The resultant force xρgA is called the upthrust and is equal to the weight of the fluid displaced by the block.
This is known as the Archimedes Principle.