Glossary

Every symbol and term used across the guides, with a link to where it’s explained.

Symbols

Symbol	Meaning	Unit	Guide
$a$, $a_t$, $a_n$	Acceleration; tangential and normal parts	m/s²	Curvilinear and circular motion
$\alpha$	Angular acceleration	rad/s²	Rigid body rotation
$B$	Thermistor β constant	K	Wheatstone bridge and thermistors
$C$	Capacitance	F	RC transients
$D$	Duty cycle, $t_{on}/T$	–	PWM
$E$	Energy	J, kWh	Electrical quantities
$E_{ON}$, $E_{OFF}$	Energy lost per MOSFET turn-on, turn-off	J	MOSFET power loss
$F_{SW}$, $F_{grid}$	Switching frequency; mains frequency (50 Hz)	Hz	PWM, AC values
$\eta$	Efficiency	%	Electrical quantities
$I$, $I_D$	Current; drain (or diode) current	A	Electrical quantities
$\mathbf{i},\mathbf{j},\mathbf{k}$	Unit vectors along x, y, z	–	Vectors
$L$	Inductance	H	DC-DC converters
$\mathbf{M}$	Moment of a force, $\mathbf{r}\times \mathbf{F}$	N m	Vectors
$\omega$	Angular velocity	rad/s	Rigid body rotation
$P$, $P_{cond}$, $P_{SW}$	Power; conduction and switching loss	W	MOSFET power loss
$Q$	Charge	C	Electrical quantities
$R$, $R_{DS(on)}$	Resistance; MOSFET on-resistance	Ω	Electrical quantities, Power switches
$R_{th}$	Thermal resistance	°C/W	Thermal design and heatsinks
${\mathbf{r}}_{B/A}$	Position of B relative to A	m	Relative motion analysis
$\rho$	Resistivity (or radius of curvature in kinematics)	Ω m	Electrical quantities
$s$, $\theta$	Position; angle	m, rad	Rectilinear motion
$\tau$	Time constant, $RC$	s	RC transients
$T_J$, $T_{amb}$	Junction temperature; ambient temperature	°C	Thermal design and heatsinks
$t_{d(on)},t_r,t_{d(off)},t_f$	MOSFET switching times	ns	MOSFET power loss
$V_{RMS}$, $V_{pk}$, $V_{avg}$	RMS, peak and average voltage	V	AC values
$V_F$	Diode forward voltage	V	Bridge rectifiers
$V_{DD}$	Supply voltage switched by a MOSFET	V	MOSFET power loss
$V_{GS(th)}$	MOSFET gate threshold voltage	V	Power switches
$V_{RRM}$	Diode’s maximum repeated reverse voltage	V	Bridge rectifiers
$\Delta V$	Ripple voltage	V	Bridge rectifiers
$K_t$, $K_e$	Motor torque constant and back-EMF constant (equal in SI)	N·m/A, V·s/rad	DC motor performance and selection
$E_b$	Back-EMF, the voltage a spinning motor generates against the supply	V	Electric motors and DC motor types
${\mu }_s$, ${\mu }_k$	Static and kinetic friction coefficients	–	Friction and Newton’s second law
$N$	Normal reaction force	N	Friction and Newton’s second law
$\bar{x}$, $\bar{y}$	Centre of mass coordinates	m	Centre of mass
$I$ (mechanics)	Mass moment of inertia; $m{r}^2$ for a particle	kg·m²	Friction and Newton’s second law
$T_h$	Stepper holding torque	N·m	Stepper motors
$C_{rr}$	Rolling resistance coefficient	–	Sizing a drive motor

Terms

Term	Meaning	Guide
ALARP	As low as reasonably practicable: reduce risk unless the cost is grossly disproportionate	Designing for safety
Back-EMF	The voltage a spinning motor generates, opposing the supply; it sets the speed	Electric motors and DC motor types
Boost / buck converter	DC-DC converters that step voltage up / down	DC-DC converters
CEng / IEng / EngTech	Professional registration titles	UK-SPEC and professional registration
Circular economy	Reuse, repair and recycle instead of make, use, dispose	Sustainability and lifecycle thinking
Couple	Two equal, opposite, parallel forces: rotation with no net force	Forces and moments
CPD	Continuing professional development	CPD and reflective practice
Cramer’s rule	Solving equations with determinants, $x_k={\Delta }_k/\Delta$	Matrices and Cramer’s rule
Determinant	A single number from a square matrix; zero means no inverse	Matrices and Cramer’s rule
Duty of care	Obligation to avoid foreseeable harm to anyone affected by your work	Engineering ethics and duty of care
Feedback loop	Balancing (seeks a goal) or reinforcing (amplifies change)	Systems thinking
Flyback diode	Diode across an inductive load to absorb the switch-off spike	Power electronics overview
FMEA	Failure modes and effects analysis, bottom-up	Designing for safety
Free body diagram	The body drawn on its own with every external force and reaction	Static equilibrium and free body diagrams
General plane motion	Translation and rotation together (e.g. a connecting rod)	Rigid body rotation
Gibbs’ cycle	Six-stage model for reflecting on an experience	CPD and reflective practice
H-bridge	Four switches that let a DC motor run both ways	Motor drives
Hazard	A potential source of harm	Hazards and risk assessment
HAZOP	Hazard and operability study, using guide words	Designing for safety
Heatsink	Part that carries heat away into the air	Thermal design and heatsinks
Hierarchy of controls	Eliminate → substitute → engineering → administrative → PPE	Designing for safety
IGBT	High-voltage transistor: MOSFET gate, BJT output	Power switches
Implicit differentiation	Differentiating an equation as it stands, with the chain rule	Implicit differentiation
Inverter	Converts DC to AC, e.g. to drive a brushless motor	Motor drives
KCL / KVL	Kirchhoff’s current and voltage laws	Kirchhoff’s laws
LCA / LCC / S-LCA	Life cycle assessment, costing and social assessment	Sustainability and lifecycle thinking
Leverage point	A place to intervene in a system; higher points are more powerful	Systems thinking
LOTO	Lock-out/tag-out: isolating energy before working on a machine	Designing for safety
Mesh analysis	Solving a circuit with one current per loop	Mesh analysis
Microstepping	Splitting a stepper’s steps by varying the phase currents	Stepper motors
MOSFET	Voltage-controlled transistor, the robotics default switch	Power switches
NTC / PTC	Thermistors whose resistance falls / rises with temperature	Wheatstone bridge and thermistors
Power balance	Check that power dissipated equals power supplied	Kirchhoff’s laws
Power utilisation	How hard a motor works compared with its rating, $P_{out}/P_{rated}$	DC motor performance and selection
Problem statement	Who has the problem, what it is and the constraints, with no solution	Writing a problem statement
PWM	Pulse width modulation: controlling average power by fast switching	PWM
Rectifier	Converts AC to DC	Bridge rectifiers
Risk register	Live list of risks, scores, controls and owners	Hazards and risk assessment
Risk	Likelihood × severity	Hazards and risk assessment
RMS	Root mean square: the heating-equivalent value of AC	AC values
Safe system of work	Written procedure for doing a task safely	Designing for safety
SMART	Specific, measurable, attainable, relevant, time-bound goals	CPD and reflective practice
Stall current	$V/R_a$: the current when a DC motor is held still	Electric motors and DC motor types
Swiss cheese model	Layered defences fail when their holes line up	Designing for safety
System architecture	The structural choices that shape a system and are hard to undo	System architecture and lifecycle
System of systems	Independently owned systems working together; nobody owns the whole	Systems thinking
Triple bottom line	People, planet, profit	Sustainability and lifecycle thinking
Two-force member	A link loaded only at its two pins, so its force acts along it	Static equilibrium and free body diagrams
UK-SPEC	The UK standard for professional engineering competence	UK-SPEC and professional registration
Voltage node method	KCL at one node to solve multi-source circuits	Voltage node method
Wheatstone bridge	Two dividers whose difference measures small resistance changes	Wheatstone bridge and thermistors