Alphabet of Engineering Units are the alphabet of engineering. Those who do not fully understand the units cannot engineer them. It may be asked whether it is an engineer who does not understand the units. However, the number of people who became engineers without digesting the units are unfortunately in our country. There are essentially two unit systems in the world. These are; 1. SI unit system (System International) This system is the most widely used system in the world and will inevitably replace other unit systems in the near future. The SI unit system is based on only seven basic units. These; Unit of length Meter (m) Mass unit Kilogram (Kg) Time unit Second (s) Current unit Amper (A) Temperature unit Kelvin (K) Light intensity unit Kandil (cd) Unit of substance quantity Mole (mol) Due to the first three of these basic units (Meter-Kilogram-Second), this system is also called MKS system. All other units in the SI unit system are made from these seven basic units. BG unit system (British Gravitational) This unit system, also known as the Imperial system, is used today only in technical books of British and American origin, and some of our professors, who use these books as a source, continue to use this system in their books. BG unit system is used today mostly for pipes and pipe thread sizes in Turkey. The first three of the basic measurements used in the BG unit system are Mass, Length and Time. However, the units of the first two of these measures are different. These; Unit of mass Pound (Lb) Unit of length Feet (ft) Time unit Seconds (Sec) In this section, we will see how we derive other main units derived from the SI unit system. FORCE The first concept in engineering is FORCE. Because all mechanical and hydraulic systems are designed to transfer or convert force. The concept of force is defined by Newton's second law. Since this law is the most basic law of mechanics, it should be mentioned here. Newton's second law: The force acting on a mass is equal to the product of the mass in question and the acceleration of that mass. In short, it is F = m * a. In this formula, m = Mass (Kg), a = acceleration (m / sn2), F = Force (Kg-m / sn2) Here, instead of the unit of force (Kg-m / sn2), it is called Newton (N) for Newton, who defines this concept. Thus, F = Force (N) is used as the unit of force. The very common mistake about this unit is the wrong perception that the force created by a 1 Kg mass is 1 N. Let's use the formula of force to remove this false perception. Question: How much force is 1 Kg of mass exerted on the table? Reply: Mass: m = 1 Kg. Acceleration: a = 9.8 m / sec2 (Since we are on the earth, the mass is affected by the acceleration of gravity. If we were on the moon, the force created by this mass would be much less.) F = 1 (Kg) * 9.8 (m / sn2) = 9.8 (Kg-m / sn2) F = 9.8 N In some schools there are still teachers who use "Kilogram Force" (Kgf) as unit of force, which confuses minds with excess. If we wanted to find the above problem in terms of (Kgf), the result would be F = 1 (Kgf). However, I think this unit should only be used when buying tomatoes from the market. KiloPond (kp), which corresponds to the kilogram force, is mentioned in the German technical literature and therefore this unit is mostly used by technical men from the German school. Another important point to be noted before closing the power bet is that force is a vector value. In other words, the force has a direction as well as its size. This means that an object can only exert a force in the direction in which it is accelerating. A 1 Kg object applies a force of 9.8 Newton to the table on which it is on, but cannot apply a force to another object standing adjacent to it on the table, no matter how large its mass. In order to apply force to the adjacent object, it must be accelerated towards that object. (In fact, even if they stand side by side, the masses attract each other in direct proportion to the size of their masses and inversely proportional to the square of the distance between them. However, this gravitational force is negligible as it is very small compared to the gravitational force of the earth. BUSINESS As we have known since high school years, the definition of the job is Force X Road. So no matter how burdened you are, if you are not getting any progress, then you are not doing anything. If we write the job description in units W = F (N) * L (m) = F * L (N-m) In this formula, F = Force (N), L = Path (m), W = Work (N-m). In memory of the British scientist Joule, who discovered that the work done produces heat, or conversely, heat can produce work, this unit is called (Joule) instead of (N-m). Thus, W = Work (J) is used as the unit of work. POWER The definition of power is briefly; It means the work produced per unit time. If we formulate it is POWER = WORK / TIME. So the sooner you do a certain job, the stronger you are. Let's replace the units in this formula. P = W (J) / T (sn) = 

W / T (J / sec) becomes

In this formula, W = Work (J), T = Time (sec), P = Power (J / sec)

If we formulate power in terms of force

Power = Force * Speed

P = F (N) * V (m / s)

P = F * V (N-m / sn) => again P = F * V (J / sn)

As in the previous definitions, in this definition, in reference to James Watt, the inventor of the steam engine, the unit of power is called (Watt) instead of (J / sec).

Thus, P = Power (W) is used as the unit of power.

ENERGY
The capacity to use power for a certain period of time is called Energy. If we formulate this definition, ENERGY = POWER * TIME. So the longer you can use your power, the more energy you have.

In the definition of energy, usually 1000 Watt, ie 1 Kilowatt, is used as power, and 3600 seconds or 1 hour as time. When calculating the amount of electrical energy we use in homes in terms of KW-Hour, when it comes to large amounts of energy used in a country, MegaWatt or GigaWatt is used as power in the Energy unit. Substituting the units in the formula

E = Ῥ (Kw) * Ƭ (hour) = Ῥ * Ƭ (Kw-Hour)

In this formula Ῥ = Power in kilowatt units (KW), Ƭ = Time in units of hours (Hours)

We obtained the power by dividing the work by time, and we obtained the energy by multiplying the obtained power with time again. That is, energy and work are identical as units. The point I want to draw your attention to here is that the more energy you spend, the more work you will do (of course, if you work with 100% efficiency!)

In heat calculations, more calories are used as energy units. The calorie is the easiest unit of energy to understand and is described as the amount of energy required to increase the temperature of 1 gram of water by 1 C.

PRESSURE
Pressure is the effect that occurs when a certain force is spread homogeneously over a certain area.
It is formulated as PRESSURE = FORCE / FIELD. If we write this formula in units.

PRESSURE p = F (N) / A (m2) = F / A (N / m2)

In this formula, F = Force (N), A = Area (m2), p = Pressure (N / m2)

The unit of this definition was called Pascal (Pa) instead of N / m2 as the unit of pressure in memory of Pascal, who explained the principles of hydraulic lifting.

Thus, Pascal (pa) is used as the pressure unit for gases and liquids as 100,000 pascals = 1 bar, since the atmospheric pressure is only 1 in 100,000, although it is the basic pressure unit in the SI unit system. (bar is originally shortened from baros, which means weight in ancient Greek).

For the pressure unit, especially when it comes to pumps, the "head" Meter is used. It may seem odd to use a measure of length as a unit of pressure. However, what is meant by the meter here is the pressure created by the water column at that height at the base. For example: 10 meters of water column (mSS) corresponds to approximately 1 bar of pressure.

Thus p = Pressure (N / m2) = 1 (Pa) = 1X10-5 bar

TEMPERATURE
The scientist who discovered that the absolute zero degree, that is the temperature at which all the movements existing in the universe stop even at the atomic level, is 273.15 degrees lower than the freezing temperature of water, Kelvin (K) has been accepted as the unit of temperature in reference to Lord Kelvin. However, as the temperature is taken as the reference one-hundredth of the difference between the freezing temperature and the boiling temperature of the water, and this definition is used in practice as the temperature unit (0C) in reference to the name of Celsius, which was made before Kelvin.

Note: The degree symbol (0) is not used in the Kelvin temperature unit.

The unit range is (K) = (0C). However, since the starting points are different, it is necessary to add 273.15 when it is necessary to change any temperature from Celsius to Kelvin.
Example: 6.85 (0C) = 280 (K)

BASIC UNITS IN SUMMARY
The following conversions are obtained by using the basic units defined above.

1Kgf = 9.81 N

1 kp = 1Kgf (kp = kilopond)

1 kp = 9.81 N

1 Joule = 1 N-m = 1W-Sn

1 Kw-Hour = 3.6 * 106 Joules

1 Kcal = 1.16X10-3 Kw-hour = 3.97 BTU

1 (bar) = 100 (Kpa) = 1.019 (Kgf / cm2) = 0.986 Atmospheric pressure (atm) = 10.2 Meter of water column (mSS)

Of course there are many more units in the SI unit system. However, almost all of these units have been obtained using these basic units.

IMPORTANT UNIT CYCLES
We frequently encounter BG units, even though their use is gradually disappearing in the world. It would be helpful to give a few important unit conversions below.

1 KW = 1.341 HP

1Kgf = 2.2046 Lbf

1Kgf / cm2 = 14.22 psi

1bar = 14.5 psi

1 bar = 10.2 meters of water column (mSS)

1 Meter = 3.28 feet

1 donum = 1 decare = 1,000 m2

1 feet = 12 inches (finger) = 12 ″

1 inch = 25.4 mm

0C = 0.555 * (0F-32)

2ΠRadian = 3600 = 400 Grad