Unit 4: Machines and Mechanisms

Comprehensive vocabulary flashcards covering engineering problem-solving phases, mechanical advantage, mechanisms, kinematics, friction, logic control, electric circuits, and metallurgy.

Idler Gear

An intermediate gear placed between a driver and a driven gear that reverses the direction of rotation without changing the overall gear ratio.

Worm Gear

A mechanism where a driving worm (screw) turns a worm wheel at $90^{\circ}$, offering large speed reduction ($\text{GR} = \frac{\text{worm wheel teeth}}{\text{number of starts on worm}}$) and typically resisting back-driving.

Rack and Pinion

A gear system consisting of a circular pinion engaging a flat toothed rack to convert rotary motion into linear motion or vice versa (e.g., car steering).

Linear Motion

Motion in a straight line in a single direction (e.g., a conveyor belt).

Rotary Motion

Movement following a continuous circular path (e.g., a spinning wheel).

Oscillatory Motion

Swinging back and forth along a curved arc (e.g., a pendulum).

Reciprocating Motion

Continuous back-and-forth movement in a straight line (e.g., an engine piston).

Work Done

The energy transferred by a force acting across a distance in the direction of the force: $W = F \times s$, measured in joules ($\text{J}$).

Power

The rate at which work is done or energy is transformed: $P = \frac{W}{t}$, measured in watts ($\text{W}$).

Kinetic Energy ($KE$)

The energy possessed by an object due to its motion: $KE = \frac{1}{2} m v^2$, measured in joules ($\text{J}$).

Potential Energy ($PE$)

The stored gravitational energy of an object due to its elevated position: $PE = mgh$, measured in joules ($\text{J}$).

Total Mechanical Energy

The sum of kinetic and potential energy ($KE + PE$), which remains constant in an ideal system ignoring friction.

Mechanical Efficiency ($\eta$)

The percentage of work input converted to useful work output: $\eta = \frac{\text{useful output}}{\text{input}} \times 100\% = \frac{\text{MA}}{\text{VR}} \times 100\%$, which is always below $100\%$ in real machines due to friction.

Forces on an Inclined Plane

Resolution of weight ($mg$) into a component into the slope balanced by the normal force ($F_N = mg \cos(\theta)$) and a component pulling down the slope ($mg \sin(\theta)$), opposed by friction ($F_f = \mu F_N$).

Friction Force ($F_f$)

A resistive force that opposes relative motion or attempted motion between surfaces in contact, calculated as $F_f = \mu F_N$.

Normal Force ($F_N$)

The perpendicular reaction force exerted by a contact surface on an object, equal to $mg$ on horizontal ground and $mg \cos(\theta)$ on an incline of angle $\theta$.

Angle of Repose

The maximum slope angle at which an object resting on an inclined plane remains stationary without sliding: $\mu_s = \tan(\theta)$.

Static vs. Kinetic Friction

Static friction ($\mu_s$) prevents stationary objects from starting to move, whereas kinetic friction ($\mu_k$) resists moving objects; typically $\mu_k < \mu_s$.

Apparent Weight

The upward contact force a floor or scale exerts on a mass: $m(g + a)$ when accelerating upward, $m(g - a)$ when accelerating downward, and $mg$ at constant velocity.

Equations of Uniformly Accelerated Motion

The kinematic relations for constant acceleration: $v = u + at$, $v^2 = u^2 + 2as$, and $s = ut + \frac{1}{2} at^2$.

Logic Gates

Fundamental digital logic devices (AND, OR, NOT, NAND, NOR, XOR); a bubble placed on an output indicates a logical NOT inversion.

Logical Identity vs. Negation

Identity produces an output equal to the input; negation produces an output that is the inverse of the input (NOT).

AND Gate

A logic gate providing an output of $1$ only when both inputs are $1$ (truth table output: $0, 0, 0, 1$).

OR Gate

A logic gate providing an output of $1$ when either input or both inputs are $1$ (truth table output: $0, 1, 1, 1$).

NOT Gate

A single-input logic gate that outputs the inverted signal ($0 \rightarrow 1$, $1 \rightarrow 0$), symbolized by a triangle with an output circle.

NAND Gate

A NOT-AND logic combination that outputs $0$ only when both inputs are $1$ (truth table output: $1, 1, 1, 0$).

NOR Gate

A NOT-OR logic combination that outputs $1$ only when both inputs are $0$ (truth table output: $1, 0, 0, 0$).

XOR Gate

An exclusive-OR logic gate that outputs $1$ exclusively when the inputs differ from each other (truth table output: $0, 1, 1, 0$).

Truth Table Row Formula

The rule establishing that a truth table requires $2^n$ rows, where $n$ is the total number of independent inputs.

Series vs. Parallel Circuits

Series circuits maintain the same current throughout ($I$) with additive voltages ($V = V_1 + V_2$) and resistances ($R_{\text{total}} = R_1 + R_2$); parallel circuits maintain equal voltage across branches with additive currents ($I = I_1 + I_2$) and reciprocal resistances ($\frac{1}{R_{\text{total}}} = \frac{1}{R_1} + \frac{1}{R_2}$).

Ohm's Law

The law relating potential difference, electric current, and resistance: $V = IR$.

Electrical Power

The rate of electrical energy consumption or output: $P = VI$, measured in watts ($\text{W}$).

Electrical Energy

The total energy delivered over time: $E = Pt$, where $P$ is power in watts and $t$ is time in seconds, measured in joules ($\text{J}$).

Lead–Tin Phase Diagram

A binary phase diagram displaying liquidus, solidus, solvus lines, and a characteristic eutectic point at $61.9\%$ tin and $183\,^{\circ}\text{C}$.

Eutectic Reaction

An isothermal invariant reaction occurring upon cooling at the eutectic composition where liquid transforms simultaneously into two distinct solid phases: $\text{liquid} \rightarrow \alpha + \beta$.

Alpha ($\alpha$) and Beta ($\beta$) Phases (Lead–Tin)

The terminal solid solutions in the lead–tin system: $\alpha$ is a lead-rich solid solution, and $\beta$ is a tin-rich solid solution.

Hypoeutectic vs. Hypereutectic Alloys

In lead–tin alloys, hypoeutectic contains less tin than the eutectic ($< 61.9\%$) and precipitates primary $\alpha$ first; hypereutectic contains more tin ($> 61.9\%$) and precipitates primary $\beta$ first.

Complete Insolubility vs. Partial Solid Solubility

Complete solid insolubility means constituent metals cannot dissolve in each other as solids (pure solid components form); partial solubility allows each metal to dissolve a limited amount of the other (such as $\alpha$ and $\beta$ in lead–tin).

Steel Portion of the Iron–Carbon Diagram

The phase diagram region below $2.1\%$ carbon detailing austenite ($\gamma$), ferrite ($\alpha$), cementite ($\text{Fe}_3\text{C}$), and pearlite, defined by a eutectoid transition at $0.83\%$ carbon and $723\,^{\circ}\text{C}$.

Austenite

The $\gamma$-iron interstitial solid solution exhibiting a face-centred cubic (FCC) structure, stable at elevated temperatures and capable of dissolving up to approximately $2.1\%$ carbon.

Ferrite

The $\alpha$-iron phase possessing a body-centred cubic (BCC) crystal structure, stable at room temperature with minimal carbon solubility (about $0.02\%$ maximum), known for being soft and ductile.

Cementite

Iron carbide ($\text{Fe}_3\text{C}$), an extremely hard and brittle intermetallic compound containing $6.67\%$ carbon by weight.

Pearlite

A lamellar (layered) composite microstructure consisting of alternating plates of ferrite and cementite formed by the eutectoid decomposition of austenite.

Eutectoid Steel

Steel with approximately $0.83\%$ carbon that cools slowly below $723\,^{\circ}\text{C}$ to form a $100\%$ pearlite microstructure.

Hypoeutectoid Steel

Steel containing less than $0.83\%$ carbon that develops a slow-cooled microstructure of proeutectoid ferrite and pearlite.

Hypereutectoid Steel

Steel containing between $0.83\%$ and $2.1\%$ carbon that develops a slow-cooled microstructure of proeutectoid cementite (at grain boundaries) and pearlite.

Low-Carbon Steel

Steel containing $0.07\%\text{ to }0.30\%$ carbon; ductile and easily formed or welded, used in car bodies, structural plate, wire, seamless tubes, and boiler plate.

Medium-Carbon Steel

Steel containing $0.30\%\text{ to }0.60\%$ carbon balancing strength and toughness; used for shafts, axles, gears, crankshafts, forgings, and train wheels.

High-Carbon Steel

Steel containing $0.60\%\text{ to }2.0\%$ carbon; hard and wear-resistant but less ductile, used for cutting tools, springs, punches, dies, and industrial knives.

Hot Working

Mechanical deformation of metal above its recrystallisation temperature (e.g., hot rolling, forging), allowing new equiaxed grains to form without work hardening.

Cold Working

Mechanical deformation of metal below its recrystallisation temperature (e.g., cold rolling), elongating grains and causing strain hardening to increase strength while lowering ductility.

Full Annealing

A heat treatment where steel is heated into the austenite region, held, and furnace-cooled very slowly to yield coarse pearlite for maximum softness and ductility.

Process Annealing

A subcritical heat treatment heating cold-worked low-carbon steel below the lower critical temperature to recrystallise grains and recover ductility between cold-working stages.

Normalising

A heat treatment involving heating steel into the austenite phase followed by air cooling, producing finer, more uniform grains that are stronger and harder than annealed steel.

Hardening

A heat treatment process where steel is heated to the austenite region and rapidly quenched, trapping carbon in solution to transform austenite into martensite.

Quenching Cooling Rates

The standard sequence of cooling media from fastest to slowest: water quench $\rightarrow$ oil quench $\rightarrow$ air cool $\rightarrow$ furnace cool (faster rates yield harder and more brittle microstructures).

Martensite

A supersaturated, needle-like, extremely hard and brittle non-equilibrium phase produced when austenite is quenched faster than the critical cooling rate, preventing carbon diffusion.

Tempering

Reheating hardened martensitic steel to a moderate temperature below the lower critical temperature, reducing brittleness and internal stresses while restoring toughness.

Acrylonitrile Butadiene Styrene (ABS)

A polymer characterized by high heat and impact resistance, good low-temperature durability, chemical resistance, dimensional stability, and electrical insulation; used for vehicle trim, hard hats, tool casings, and pipes.

Polycarbonate (PC)

An engineering thermoplastic noted for exceptional optical transparency, high impact toughness, heat resistance, and dimensional stability; used for safety glasses, headlamp lenses, visors, and machine guards.

Nylon 6 (PA6)

A semi-crystalline polyamide featuring high tensile strength, high abrasion and fatigue resistance, and chemical durability; used for gears, rollers, bearings, wear pads, and structural fasteners.