# Introduction to Mechanical Engineering Chapter 1

__What is Mechanical Engineering?__

**Author:** Eze-Odikwa Tochukwu Jed

**Note:** All articles posted here are accurate, up-to-date and drafted from real university curriculums. Proper references will be added at the bottom of this article upon its completion. Do so kindly to reference/attribute us when copying our articles thanks.

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**College Reg Number:** MOUAU/CME/14/18475

**Definition of Mechanical Engineering**

Although every engineering faculty member in every engineering department will claim that his/her field is the broadest engineering discipline, in the case of Mechanical Engineering that’s actually true (I claim) because the core material permeates all engineering systems (fluid mechanics, solid mechanics, heat transfer, control systems, etc.)

Mechanical engineering is one of the oldest engineering fields (though perhaps Civil Engineering is even older) but in the past 20 years has undergone a rather remarkable transformation as a result of a number of new technological developments including:

**Computer Aided Design (CAD):**The average non-technical person probably thinks that mechanical engineers sit in front of a drafting table drawing blueprints for devices having nuts, bolts, shafts, gears, bearings, levers, etc. While that image was somewhat true 100 years ago, today the drafting board has long since been replaced by CAD software, which enables a part to be constructed and tested virtually before any physical object is manufactured.**Simulation:**CAD allows not only sizing and checking for fit and interferences, but the resulting virtual parts are tested structurally, thermally, electrically, aerodynamically, etc. and modified as necessary before committing to manufacturing.**Sensor and actuators:**Nowadays even common consumer products such as automobiles have dozens of sensors to measure temperatures, pressures, flow rates, linear and rotational speeds, etc. These sensors are used not only to monitor the health and performance of the device, but also as inputs to a microcontroller. The microcontroller in turn commands actuators that adjust flow rates (e.g. of fuel into an engine), timings (e.g. of spark ignition), positions (e.g. of valves), etc.**3D printing:**Traditional “subtractive manufacturing” consisted of starting with a block or casting of material and removing material by drilling, milling, grinding, etc. The shapes that can be created in this way are limited compared to modern “additive manufacturing” or “3D printing” in which a structure is built in layers. Just as CAD + simulation has led to a new way of designing systems, 3D printing has led to a new way of creating prototypes and in limited cases, full-scale production.**Collaboration with other fields:**Historically, a nuts-and-bolts device such as an automobile was designed almost exclusively by mechanical engineers. Modern vehicles have vast electrical and electronic systems, safety systems (e.g. air bags, seat restraints), specialized batteries (in the case of hybrids or electric vehicles), etc., which require design contributions from electrical, biomechanical and chemical engineers, respectively. It is essential that a modern mechanical engineer be able to understand and accommodate the requirements imposed on the system by non-mechanical considerations.

These radical changes in what mechanical engineers do compared to a relatively short time ago makes the field both challenging and exciting.

**Mechanical Engineering curriculum**

In almost any accredited Mechanical Engineering program, the following courses are required:

- Basic sciences – math, chemistry, physics
- Breadth or distribution (called “General Education” at USC)
- Computer graphics and computer aided design (CAD)
- Experimental engineering & instrumentation
- Mechanical design – nuts, bolts, gears, welds
- Computational methods – converting continuous mathematical equations into discrete equations solved by a computer
- Core “engineering science”
- Dynamics – essentially F = ma applied to many types of systems
- Strength and properties of materials
- Fluid mechanics
- Thermodynamics
- Heat transfer
- Control systems
- Senior “capstone” design project

Additionally you may participate in non-credit “enrichment” activities such as undergraduate research, undergraduate student paper competitions in ASME (American Society of Mechanical Engineers, the primary professional society for mechanical engineers), the Formula SAE racecar project, etc.

**Nomenclature**

Symbol | Meaning | SI units and/or value |

A | Area | m^{2} |

BTU | British Thermal Unit | 1 BTU = 1055 J |

C_{D} | Drag coefficient | |

C_{L} | Lift coefficient | |

C_{P} | Specific heat at constant pressure | J/kgK |

C_{V} | Specific heat at constant volume | J/kgK |

c | Sound speed | m/s |

COP | Coefficient Of Performance | |

d | Diameter | m (meters) |

E | Energy | J (Joules) |

E | Elastic modulus | N/m^{2} |

e | Internal energy per unit mass | J/kg |

F | Force | N (Newtons) |

f | Friction factor (for pipe flow) | |

g | Acceleration of gravity | m/s^{2 }(earth gravity = 9.81) |

g_{c} | USCS units conversion factor | 32.174 lbm ft/ lbf sec^{2} = 1 |

H | Convective heat transfer coefficient | W/m^{2 }K |

Ι | Area moment of inertia | m^{4} |

Ι | Electric current | amps |

k | Boltzmann’s constant | 1.380622 x 10^{-23} J/K |

k | Thermal conductivity | W/mK |

L | Length | m |

m | Molecular Mass | kg/mole |

M | Moment of force | N m (Newtons x meters) |

M | Mach number | |

m | Mass | kg |

m | Mass flow rate | kg/s |

n | Number of moles | |

N_{A} | Avogadro’s number (6.0221415 x 10^{23}) | |

P | Pressure | N/m^{2} |

P | Point-load force | N |

Q | Heat transfer | J |

q | Heat transfer rate | W (Watts) |

R_{e} | Reynolds number | |

R | Electrical resistance | ohms |

r | Radius | m |

S | Entropy | J/K |

T | Temperature | K |

T | Tension (in a rope or cable) | N |

t | Time | J |

U | Internal energy | J |

u | Internal energy per unit mass | J/kg |

V | Volume | m^{3} |

V | Voltage | Volts |

V | Shear force | N |

v | Velocity | m/s |

W | Weight | N (Newtons) |

W | Work | J |

w | Loading (e.g. on a beam) | N/m |

Z | Thermoelectric figure of merit | 1/K |

z | elevation | m |

R | Universal gas constant | 8.314 J/mole K |

α | Thermal diffusivity | m^{2}/s |

γ | Gas specific heat ratio | |

η | Efficiency | |

ε | Strain | |

ε | Roughness factor (for pipe flow) | |

µ | Coefficient of friction | |

µ | Dynamic viscosity | kg/m s |

θ | Angle | |

ν | Kinematic viscosity = µ/ρ | m^{2}/s |

ν | Poisson’s ratio | |

ρ | Density | kg/m^{3} |

ρ | Electrical resistivity | ohm m |

σ | Normal stress | N/m^{2} |

σ | Stefan-Boltzmann constant | 5.67 x 10^{-8} W/m^{2}K ^{4} |

σ | Standard deviation | [Same units as sample set] |

τ | Shear stress | N/m^{2} |

τ | Thickness (e.g. of a pipe wall) | m |

Type | SI unit | USCS unit | Other conversions |

Base units | |||

Length | meter (m) | 3.281 foot (ft) = 1 m | 1 m = 100 centimeters (cm) = 1000 millimeters (mm) = 39.37 inches (in) 1 kilometer (km) = 1000 m 1 mile (mi) = 5280 ft |

Mass | kilogram (kg) | 2.205 pounds mass (lbm) = 1 kg | 1000 grams (g) = 1 kg 1 slug = 32.174 lbm |

Time | second (s) | s | 1 minute (min) = 60 s 1 hour (hr) = 60 min |

Charge | coulomb (coul) | coul | 1 coul = charge on 6.241506 x 10^{18} electrons |

Derived units | |||

Area (length^{2 }) | m^{2} | 10.76 ft^{2} = 1 m^{2} | 1 acre = 43,560 ft^{2} 640 acres = 1 mi ^{2} 1 hectare = 10,000 m ^{2} = 2.471 acre |

Volume (length^{3} ) | m^{3} | 35.32 ft^{2} = 1 m^{3} | 1 ft^{3} = 7.48 gallons (gal) = 28,317 cm ^{3} (ml, cc) 1 m ^{3} = 264.2 gal 1 liter = 0.001 m ^{3} = 1000 cm ^{3} = 61.02 in ^{3} |

Velocity (length/time) | m/s | 3.281 ft/s = 1 m/s | 60 mi/hr = 88 ft/s |

Acceleration (length/time^{2 }) | m/s^{2} | 3.281 ft/s^{2 }= 1 m/s^{2} | 1 g (standard earth gravity) = 9.806 m/s ^{2} = 32.174 ft/s^{2} |

Force = mass×length/time^{2} | 1 Newton (N) = 1 kg m/s^{2} | 1 pound force (lbf) = 4.448 N | 1 dyne = 1 g cm/s^{2} = 10^{-5} N |

Energy = mass×length^{2}/ time^{2} | 1 Joule (J) = 1 kg m^{2} /s^{2} = 1 Nm | 1 J = 0.7376 (ft lbf) (foot-pound) | 1 British Thermal Unit (BTU) = 1055 J = 778 ft lbf 1 calorie (cal) = 4.184 J 1 diet calorie = 1000 cal 1 erg = 1 g cm ^{2} /s^{2} = 10^{-7} J |

Power = mass×length^{2}/time^{3} | 1 Watt (W) = 1 kg m^{2} /s^{3} = 1 Nm/s | 1 horsepower (hp) = 746 W | 1 hp = 550 ft lbf/s |

Temperature | Kelvin (K) | 1.8 Rankine (R) = 1 K | |

Heat capacity = Energy/ mass × temperature | 1 J /kg K = 1 J/kg˚C | 1 BTU/lbm˚F = 1 BTU/lbmR = 1 cal/g˚C | (Note: that’s not a misprint, the conversion factor between BTU/lbm˚F and cal/g˚C is exactly 1) |

Current = charge/time | 1 Ampere (A or amp) = 1 coul/s | 1 milliamp (mA) = 0.001 A | |

Voltage = energy/charge | 1 Volt (V) = 1 J/coul | ||

Capacitance = coul/Volt | 1 Farad (f) = 1 coul/Volt = 1 coul^{2} /J | 1 microfarad (µf) = 10^{-6} f 1 picofarad (pf) = 10 ^{-12} f | |

Inductance = Volt / (amp/s) | 1 Henry (H) = 1 J s^{2} /coul^{2} | 1 millihenry (mH) = 0.001 H | |

Resistance = Volt/amp | 1 Ohm (Ω) = 1 Volt/amp = 1 J s/coul2 |

**Temperature conversion formulae:**

Kelvins (K, not ˚K) is the absolute temperature scale in SI units.

Rankines (R, not ˚R) is the absolute temperature scale in USCS units.

T (in units of ˚F) = T (in units of R) – 459.67

T (in units of ˚C) = T (in units of K) – 273.15

T (in units of ˚C) = [T (in units of ˚F) – 32]/1.8

T (in units of ˚F) = 1.8[T (in units of ˚C)] + 32

1K of temperature change = 1˚C of temperature change = 1.8˚F of temperature change = 1.8R of temperature change.

**Revolution conversion formulae:**

1 revolution = 2π radians = 360 degrees

**Ideal gas law** – note that there are many “flavors” of the ideal gas law:

PV=n**R**T

PV=mRT

Pv=RT

**P = ρRT** – most useful form for engineering purposes; more useful to work with mass than moles, because moles are not conserved in chemical reactions!

P = pressure (N/m^{2} );

V = volume (m^{3} );

n = number of moles of gas

**R** = universal gas constant (8.314 J/moleK);

T = temperature (K) m = mass of gas (kg);

R = mass-specific gas constant = R/M

M = gas molecular mass (kg/mole);

v = V/m = specific volume (m^{3} /kg)

ρ = 1/v = density (kg/m^{3} )

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