PRESSURE IN LIQUIDS

Shelly, Sarah, Syaqeerah, Tania, Aisya

Definition Of Liquid Pressure

• Refers to the pressure exerted by a fluid. It is directly proportional to the specific gravity at a specific point and to the height of the fluid above that point.

• When you swim, you can feel the pressure acting on your ear drum. Why ?

• The deeper you swim the greater the pressure. At greater depth, the weight of the liquid above contributes to the pressure.

• The deeper the point, the greater the weight of the liquid above.

Characteristics of Liquid Pressure

Pressure increases with depth

• The deeper the liquid, the further the liquid spurts out.

• In conclusion, the pressure in a liquid increases with

depth.

Pressure acts in all direction

• The pressure at any point of a liquid acts equally in all direction.

Pressure in liquid does not depends on the size/shape of the container

h

*since h is the same

the area of its surface

h h

The pressure is the same at the bottom.*since h is the same.

Pressure at 2 points at the same level in the same liquid are equal• When the container is drilled with several

indentical holes at the same height, water will spurt out at the equal speeds to reach equal distances from the circumference of the base.

• The level of the surface of a liquid in a container is always the same because for a given liquid, the pressure is always equal at the same level.

Pressure depends on the vertical depth, but not the length of liquid column

P A = P B*since they are at the same vertical distance, h , from the surface of liquid

Deriving the formula for pressure in liquid

P

A

Uniform column

Liquid density, ρh

Liquid surface

A = Area of baseh = Depth of baseG = Gravitational field strengthρ = Density of liquid

1. Figure shows a column of liquid of density, ρ in the form of a cuboid with a depth, h below the surface of the liquid, and base area, A.

2. The force acting on the base of the surface area, A is the weight of the column of liquid above it.

3. The formula for the pressure at a depth, h in the liquid can be derived as follows:

3. The formula for the pressure at a depth, h in the liquid can be derived as follows:

Volume of liquid column, V = Ah Mass of liquid column, m = ρV = AhρWeight of liquid column, W= mg = Ahρg

The force acting on the surface area A is the weight of the liquid column above it

Pressure, P = weight of liquid column Area of the base of liquid column = W A =Ahρg A P = hρg

4. The SI unit of pressure is pascal (Pa), which is equivalent to 1N m-2, If h is measured in metres (m), m-2 in kg m-3, anf g in N kg-1

Application of Pressure in liquids

The Dam

• You can see from the diagram that the dam is much thicker at the bottom than it is at the top.

• This is because the pressure of the water is much greater deeper down and the dam needs to be thick at the bottom so that it is strong enough to withstand this larger pressure.

Siphon• In the water siphon the

water will flow out of the end of the tube A. If a hole is made in the tube at P air will get in and the links between the water molecules will be broken and the flow will stop.

• A siphon is useful for emptying ponds, water tanks etc. where you need to make the water 'flow uphill' at the start.

THANK YOU