Title: Mechanical Engineering Basics — LearnCoachAssist

Q: What is the first condition of equilibrium in statics?
A: The sum of all forces acting on a body must equal zero: ΣF = 0.

Q: What is the second condition of equilibrium in statics?
A: The sum of all moments about any point must equal zero: ΣM = 0.

Q: What is a free body diagram (FBD)?
A: A sketch of a body isolated from its surroundings showing all external forces and moments acting on it.

Q: What is a statically determinate structure?
A: A structure where all unknown reactions can be found using the equations of equilibrium alone.

Q: What is the difference between a roller support and a pin support?
A: A roller provides one reaction force (normal to surface); a pin provides two reaction forces (horizontal and vertical).

Q: Define the moment of a force about a point.
A: M = F × d, where F is the force magnitude and d is the perpendicular distance from the point to the line of action.

Q: What is a couple in statics?
A: Two equal, opposite, and non-collinear forces that produce a pure rotational effect (moment) with no net translational force.

Q: What is the centroid of a body?
A: The geometric center of an area or volume; the point where the body would balance perfectly if supported there.

Q: What is the moment of inertia (second moment of area)?
A: A geometric property I = ∫y² dA that measures a cross-section's resistance to bending.

Q: What is the parallel axis theorem?
A: I = I_c + Ad², where I_c is the moment of inertia about the centroid, A is area, and d is the distance between axes.

Q: What is Newton's First Law of Motion?
A: A body remains at rest or in uniform motion unless acted upon by a net external force.

Q: What is Newton's Second Law of Motion?
A: The net force on a body equals its mass times acceleration: F = ma.

Q: What is Newton's Third Law of Motion?
A: For every action there is an equal and opposite reaction: F₁₂ = −F₂₁.

Q: Define linear momentum.
A: The product of mass and velocity: p = mv. It is a vector quantity.

Q: State the work-energy theorem.
A: The net work done on a body equals the change in its kinetic energy: W_net = ΔKE = ½mv₂² − ½mv₁².

Q: What is the impulse-momentum theorem?
A: The impulse (force × time) equals the change in momentum: FΔt = Δ(mv).

Q: What is the difference between kinetics and kinematics?
A: Kinematics describes motion without regard to forces; kinetics relates forces to the resulting motion.

Q: Define angular velocity.
A: The rate of change of angular displacement: ω = dθ/dt, measured in rad/s.

Q: What is centripetal acceleration?
A: Acceleration directed toward the center of a circular path: a_c = v²/r = ω²r.

Q: What is D'Alembert's principle?
A: By adding an inertial force −ma to a dynamic system, it can be analyzed as if in static equilibrium.

Q: State the Zeroth Law of Thermodynamics.
A: If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other.

Q: State the First Law of Thermodynamics.
A: Energy cannot be created or destroyed; for a closed system: ΔU = Q − W (change in internal energy = heat added minus work done).

Q: State the Second Law of Thermodynamics (Clausius statement).
A: Heat cannot spontaneously flow from a colder body to a hotter body without external work.

Q: State the Second Law of Thermodynamics (Kelvin-Planck statement).
A: No heat engine can convert all absorbed heat into work; some heat must be rejected to a cold reservoir.

Q: State the Third Law of Thermodynamics.
A: The entropy of a perfect crystal approaches zero as the temperature approaches absolute zero (0 K).

Q: Define enthalpy.
A: A thermodynamic property defined as H = U + PV, representing internal energy plus flow work.

Q: What is entropy?
A: A measure of molecular disorder or energy dispersal in a system: dS = δQ_rev / T.

Q: What is the Carnot efficiency?
A: The maximum efficiency of a heat engine operating between two temperatures: η = 1 − T_cold/T_hot (temperatures in Kelvin).

Q: What is an adiabatic process?
A: A process in which no heat is transferred between the system and its surroundings (Q = 0).

Q: What is an isothermal process?
A: A process that occurs at constant temperature (ΔT = 0).

Q: Define specific heat capacity.
A: The amount of heat required to raise the temperature of a unit mass by one degree: c = Q/(mΔT).

Q: What is the ideal gas law?
A: PV = nRT, where P is pressure, V is volume, n is moles, R is the universal gas constant, and T is absolute temperature.

Q: Define density in fluid mechanics.
A: Mass per unit volume: ρ = m/V, typically in kg/m³.

Q: What is Pascal's Law?
A: Pressure applied to a confined fluid is transmitted equally in all directions throughout the fluid.

Q: State Archimedes' Principle.
A: A body immersed in a fluid experiences a buoyant force equal to the weight of the fluid displaced.

Q: What is the continuity equation for incompressible flow?
A: A₁v₁ = A₂v₂; the product of cross-sectional area and velocity is constant along a streamline.

Q: State Bernoulli's equation.
A: For steady, incompressible, inviscid flow: P + ½ρv² + ρgh = constant along a streamline.

Q: What is the Reynolds number?
A: A dimensionless number Re = ρvD/μ that predicts whether flow is laminar or turbulent.

Q: At what Reynolds number does pipe flow typically transition from laminar to turbulent?
A: The critical Reynolds number for pipe flow is approximately Re ≈ 2300.

Q: What is viscosity?
A: A fluid's internal resistance to flow; dynamic viscosity (μ) relates shear stress to velocity gradient: τ = μ(dv/dy).

Q: What is the difference between laminar and turbulent flow?
A: Laminar flow has smooth, orderly layers; turbulent flow has chaotic, irregular fluctuations and higher mixing.

Q: Define stress in materials science.
A: Force per unit area acting on a material: σ = F/A, measured in Pascals (Pa).

Q: Define strain in materials science.
A: The ratio of deformation to original length: ε = ΔL/L₀ (dimensionless).

Q: State Hooke's Law.
A: Within the elastic limit, stress is proportional to strain: σ = Eε, where E is Young's modulus.

Q: What is Young's modulus (modulus of elasticity)?
A: The ratio of normal stress to normal strain in the elastic region: E = σ/ε, measured in Pa.

Q: What is Poisson's ratio?
A: The ratio of lateral strain to axial strain: ν = −ε_lateral/ε_axial, typically 0.25–0.35 for metals.

Q: What is shear stress?
A: Stress acting parallel (tangential) to a surface: τ = V/A, where V is the shear force.

Q: What is the shear modulus (modulus of rigidity)?
A: The ratio of shear stress to shear strain: G = τ/γ.

Q: What is the relationship between E, G, and ν?
A: G = E / [2(1 + ν)], linking Young's modulus, shear modulus, and Poisson's ratio.

Q: What is the yield strength of a material?
A: The stress at which a material begins to deform plastically (permanently) rather than elastically.

Q: What is ultimate tensile strength (UTS)?
A: The maximum stress a material can withstand before necking begins in a tensile test.

Q: Define factor of safety.
A: The ratio of a material's failure strength to the actual applied stress: FoS = σ_failure / σ_actual.

Q: What is fatigue failure?
A: Failure that occurs under repeated cyclic loading at stress levels below the material's static ultimate strength.

Q: What is creep?
A: Time-dependent, permanent deformation of a material under constant stress at elevated temperature.

Q: What is thermal expansion?
A: The tendency of a material to change dimensions with temperature: ΔL = αL₀ΔT, where α is the coefficient of thermal expansion.

Q: What are the three modes of heat transfer?
A: Conduction (through a solid), convection (via fluid motion), and radiation (via electromagnetic waves).

Q: State Fourier's Law of heat conduction.
A: The heat flux is proportional to the negative temperature gradient: q = −k(dT/dx), where k is thermal conductivity.

Q: What is Newton's Law of Cooling (convection)?
A: Heat transfer rate by convection: Q = hA(T_s − T_∞), where h is the convection coefficient.

Q: State the Stefan-Boltzmann Law for radiation.
A: Radiant heat from a black body: Q = σεAT⁴, where σ = 5.67×10⁻⁸ W/m²K⁴ and ε is emissivity.

Q: What is thermal conductivity?
A: A material property measuring its ability to conduct heat: k, in units of W/(m·K). Metals have high k; insulators have low k.

Q: What is the overall heat transfer coefficient (U)?
A: A single value combining conduction, convection, and fouling resistances: Q = UAΔT.

Q: Define a heat exchanger's LMTD.
A: Log Mean Temperature Difference: LMTD = (ΔT₁ − ΔT₂) / ln(ΔT₁/ΔT₂), used to calculate heat exchanger performance.

Q: What is a keyway in machine design?
A: A slot machined into a shaft and hub to receive a key that transmits torque between them.

Q: What is the purpose of a flywheel?
A: To store rotational kinetic energy and smooth out fluctuations in angular velocity during a machine cycle.

Q: What is a gear ratio?
A: The ratio of the number of teeth (or diameters) of two meshing gears: GR = N₂/N₁ = ω₁/ω₂.

Q: What is the function of a bearing in machine design?
A: To reduce friction and support loads between moving parts (shaft and housing).

Q: What is the difference between a journal bearing and a rolling-element bearing?
A: A journal bearing uses a fluid film for sliding contact; a rolling-element bearing uses balls or rollers to reduce friction.

Q: What is a spring constant (stiffness)?
A: The ratio of applied force to displacement: k = F/δ, in N/m. Higher k means a stiffer spring.

Q: How do springs combine in series?
A: The equivalent stiffness is: 1/k_eq = 1/k₁ + 1/k₂ + … (lower than any individual spring).

Q: How do springs combine in parallel?
A: The equivalent stiffness is: k_eq = k₁ + k₂ + … (stiffer than any individual spring).

Q: What is the critical speed of a shaft?
A: The rotational speed at which a shaft's natural frequency of vibration matches the operating speed, risking resonance.

Q: What is a power screw used for?
A: To convert rotary motion into linear motion (or vice versa) and transmit power, e.g., in jacks and presses.

Q: What is the mechanical advantage of a lever?
A: The ratio of output force to input force: MA = F_out/F_in = d_in/d_out (distance ratio).

Q: Define torque.
A: The rotational equivalent of force: T = F × r, where r is the perpendicular distance from the axis of rotation.

Q: What is the relationship between power, torque, and angular velocity?
A: P = Tω, where P is power (W), T is torque (N·m), and ω is angular speed (rad/s).

Q: What is the torsion formula for a circular shaft?
A: τ = Tr/J, where T is torque, r is radial distance, and J is the polar moment of inertia.

Q: What is the flexure formula for beam bending?
A: σ = My/I, where M is bending moment, y is distance from neutral axis, and I is moment of inertia.

Q: What is casting as a manufacturing process?
A: Pouring molten metal into a mold and allowing it to solidify into the desired shape.

Q: What is forging?
A: Shaping metal using compressive forces, typically with a hammer or press, to improve grain structure and strength.

Q: What is the difference between hot working and cold working?
A: Hot working is performed above the recrystallization temperature; cold working is below it and increases hardness via strain hardening.

Q: What is turning on a lathe?
A: A machining process where a workpiece rotates against a stationary cutting tool to produce cylindrical shapes.

Q: What is milling?
A: A machining process using a rotating multi-point cutter to remove material from a stationary workpiece.

Q: What is welding?
A: A fabrication process that joins materials by applying heat, pressure, or both to fuse them together.

Q: What is the difference between MIG and TIG welding?
A: MIG (GMAW) uses a consumable wire electrode and is faster; TIG (GTAW) uses a non-consumable tungsten electrode for more precise welds.

Q: What is powder metallurgy?
A: A process of making parts by compacting metal powder in a die and then sintering (heating below melting point) to bond particles.

Q: What is injection molding?
A: A manufacturing process where molten plastic is injected into a mold cavity under high pressure, then cooled to form the part.

Q: What is hardness in materials science?
A: A material's resistance to localized plastic deformation (indentation or scratching), measured by Brinell, Rockwell, or Vickers tests.

Q: What is the difference between brittle and ductile fracture?
A: Brittle fracture occurs suddenly with little plastic deformation; ductile fracture involves significant plastic deformation before breaking.

Q: What is an alloy?
A: A mixture of two or more elements, at least one being a metal, designed to achieve improved mechanical or chemical properties.

Q: What are ferrous metals?
A: Metals and alloys that contain iron as the primary element, such as steel and cast iron.

Q: What is the SI unit of force?
A: The Newton (N), defined as 1 kg·m/s².

Q: What is the SI unit of pressure?
A: The Pascal (Pa), defined as 1 N/m².

Q: What is the SI unit of energy and work?
A: The Joule (J), defined as 1 N·m.

Q: What is the SI unit of power?
A: The Watt (W), defined as 1 J/s.

Q: How many Pascals are in 1 bar?
A: 1 bar = 100,000 Pa (10⁵ Pa).

Q: How many pounds-force are in 1 Newton?
A: 1 N ≈ 0.2248 lbf.

Q: What is 1 horsepower in watts?
A: 1 hp ≈ 745.7 W.

Q: How do you convert Celsius to Kelvin?
A: K = °C + 273.15.

Q: What is 1 BTU in joules?
A: 1 BTU ≈ 1055.06 J.

Q: What is 1 atmosphere in Pascals?
A: 1 atm = 101,325 Pa.