# Pressure Of Liquids

## Physics lesson, pressure subject. Pressure exerted to the bottoms and walls of the container by a static liquid in a container. The pressure of the static liquids. The liquid pressure force.

**Pressure In Liquids**

Liquids fill the container they are in. Due to liquids have a weight, they are exert a pressure to the bottoms and sides of containers which they are located.

Pressure: The force applied on unit surface area is called pressure.

Pressure Force: The force applied on a surface is called pressure force.

The pressure force is multiplication of the pressure and surface area.

**Pressure Formula**

The pressure is the applied force, per unit area, its formula is as following.

P = ρ•g•h

P: Pressure

ρ: density of liquid

g: Acceleration of gravity

If the force exerted to the surface and the surface area are known, the pressure can be found from the formula follows.

P = | F | |

A |

P: Pressure

F: Pressure force

A: Surface area

According to International System of Units (SI), the unit of the pressure is Pascal (Pa).

1 Pa = | 1 N | |

1 m^{2} |

The pressure is a scaler magnitude.

**Example:**

A tank was filled with a liquid having a density of 820 kg /m3.

Calculate the pressure exerted at a depth of 180 cm from upper surface of the liquid tank.

**Solution:**

P = d•g•h

P = 820 • 9.8 • 1,8

P = 14464.8 Pascal

**Example:**

In the figure above is seen the K and L tanks that have linked together. The liquid, can moves freely in the tanks. The liquids are the same.

The density of liquid is 0.9 g/cm^{3}.

The height of the L tank is 2.5 m.

The height of the K tank is 3.5 m.

The pressure at point P_{A} is P1, the pressure at point P_{B} is P2.

Calculate the P1 and the P2.

(g = 10 m/s^{2})

**Solution:**

The formula that gives the pressure at any point.

P = ρ•g•h

0.9 g/cm^{3} = 900 kg/m^{3}

The pressure on point P_{A}.

P1 = 900 • 10 • 3.5

P1 = 31500 Pa

The pressure on point P_{B}.

P2 = 900 • 10 • 6

P2 = 54000 Pa

**The Pressure Force Of Liquids**

It is checked whether the pressure is the same at each point of the surface.

If is asked pressure exerted on the smooth bottom of the container, the pressure exerted to the bottom of the container is multiplied by the bottom surface area of the container.

If pressure is exerted on the container’s side surfaces, the average of the pressure exerted to the side surface of the container is multiplied by the side surface area of the container.

The average pressure on the side surface of the container is the pressure calculated by taking 1 /2 of the side surface height.

For example, if the height of the container is h, average pressure is

P_{avg} = ρ•g•h/2

**Example**

The L container that seen in the figure above was filled with a liquid having density of 0,85 g/cm^{3}.

Find average pressure and pressure force on the "A" surface.

(g = 10 m/s^{2})

**Solution:**

The width of the A surface is 3 m and the height is 4 m.

The height of the liquid in L container is 4 m. The average pressure at "A" surface is found taking h = 2 m.

0,85 g/cm^{3} = 850 kg/m^{3}

Port = 850 • 10 • 2

Port = 17000 Pa

The pressure force ont "A" surface.

S = 3•4

S = 12 m^{2}

F = 17000 • 12

F = 204000 N

RISE KNOWLEDGE

25/07/2018

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