**0**

MASS & WEIGHT

Mass and weight are not the same thing.Mass is defined as the. The standard unit of mass is

amount of matter an object contains

the pound (lbm) kilograms (kg).

Weightis the measure of gravitational force exerted upon an object.

Weight is measured in a unit called the pound-force (lbf) Newton (N),

which describes the mass of an object multiplied by the acceleration

due to gravity:

Gravitational Force = mass [lbm] ´ acceleration due to gravity [ft/s2]

= mass [kg] ´ acceleration due to gravity [m/s2]

W =m•

[g][lbm] • [ft]

=

[kg • m]

= [N]

[gc] [s2] [s2]

where

m =lbm

(mass)

=kg (mass)

g = acceleration due to gravity (32.174 ft/s2)

= acceleration due to gravity (9.8 m/s2)

gc = conversion factor

32.174 lbm • ft/s2

lbf

As a matter of convenience, the mass of an object on the earth’s

surface is equated to the object’s weight, so that the measure of an

object’s mass and the measure of an object’s weight are often used

interchangeably. When we move off the earth’s surface, the difference

between mass and weight is more apparent. Consider a person

whose mass is 119 lbm (54 kg) on the surface of the earth. If that

person goes to the moon, where the gravitational force is 1/6 as much

as it is on earth, his mass will not change. A person with a mass of

119 lbm (54 kg) weighs 119 lbf (529.5 N) on earth, where the acceleration

due to gravity is 32.174 ft/s2 (9.8 m/s2) (at sea level and

45º latitude):

Gravitational force

(weight) = mass ´ acceleration

= 119 lbm ´ (32.174 ft/s2) ´ 1 lbf

32.174 lbm • ft/s2

=54 kg ´ (9.8 m/s2)

= 119 lbf

= 529.2 N

On the moon, where the acceleration due to gravity is 5.25 ft/s2

(1.6 m/s2), the same person with a mass of 119 lbm (54 kg) weighs

19.4 lbf (86.4 N):

Gravitational force (weight) = mass ´ acceleration

= 119 lbm ´ (5.25 ft/s2) 1 lbf

32.174 lbm • ft/s2

=54 kg ´ 1.6 m/s2

= 19.4 lbf

= 86.4 N

On a daily basis, density and viscosity are the most important factorsmovement of liquid in the pipeline.

affecting line operation. They account for most line pressure changes

and, subsequently, for most of the operators’ actions to control the

VISCOSITY

On a daily basis, density and viscosity are the most important factors

affecting line operation. They account for most line pressure changes

and, subsequently, for most of the operators’ actions to control the

movement of liquid in the pipeline.Viscosityis defined as the property of a liquid which describes its

resistance to flow, or as the measure of a liquid’s internal friction.

A liquid with high viscosity will not flow or pour as easily as a liquid

with low viscosity. Honey, for example, has a much higher viscosity

than water. Because honey has a higher viscosity than water, honey

tends to change shape much less easily and flow much more slowly

than water.

Viscosity and density are not related. Two liquids may have the same

density but very different measures of viscosity. For example,

mercury is quite dense but has low viscosity. The energy needed to

overcome pipeline friction is one of the most significant costs in

operating a pipeline.

When liquid moves down the pipeline there is friction between the

liquid at the pipe wall and the pipe wall itself. This friction slows

down the liquid along the pipe wall. The higher a liquid’s viscosity,

the more friction there will be against the pipe wall.

Fluidity is the opposite of viscosity. While viscosity is the property of

a liquid which describes its resistance to flow,fluidityis the capacity. A liquid with high viscosity can also be said to

of a liquid to flow

have a low fluidity; conversely, a liquid with low viscosity can also be

said to have a high fluidity.

the line pressure between two pump stations, Aflow.

and B. The initial pressure at A is dictated by the required suction

pressure at B and depends on the density of the liquid. Pressure is lost

between the two stations in overcoming the frictional resistance to

#### من مواضيع المحجوب توتي :

التفكير الايجابي في الحياة

Factors affecting pipeline performance

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كتب أستاذ انكليزي العبارة التالية على السبورة

طلب كتاب Thermodynamics: Concepts and...

كورس تطوير مهارة الاقرائة , الاستماع و التحدث

الانكليزية لكل العرب

الازحه والحموله

موقع رائع جدا متخصص للكتابات بمختف انواعها

للتسجيل في الشات باللغه الانجليزيه

Factors affecting pipeline performance

برنامج تعليم التحدث باللغة الانجليزية رائع...

كتب أستاذ انكليزي العبارة التالية على السبورة

طلب كتاب Thermodynamics: Concepts and...

كورس تطوير مهارة الاقرائة , الاستماع و التحدث

الانكليزية لكل العرب

الازحه والحموله

موقع رائع جدا متخصص للكتابات بمختف انواعها

للتسجيل في الشات باللغه الانجليزيه

التعديل الأخير تم بواسطة المحجوب توتي ; 2009-08-15 الساعة 07:06 PM