AMIE Section B Mechanical key terms

The principle that every term in a valid physical equation must carry identical base dimensions, allowing equations to be checked and unknown relationships to be derived by balancing mass, length, time and temperature.

A method that groups the variables of a physical problem into dimensionless products, reducing the number of independent variables needed to describe the behaviour being studied.

A dimensionless ratio of inertial to viscous forces in a flow, used to predict whether flow remains laminar or becomes turbulent and to scale model tests to prototypes.

A drawing method in which parallel projectors meet the plane of projection at right angles, producing front, top and side views that show true shape and size.

A projection convention in which the object sits between the observer and the plane, so the view seen from the front is placed below the front view on the sheet.

A drawing in which part of the object is imagined cut away and the cut surface is hatched, revealing internal features such as holes and bores that hidden lines would otherwise show.

The system of tolerances that defines the permissible size range of mating parts and the resulting clearance or interference between a hole and its shaft.

A permitted deviation from an ideal shape, orientation, location or runout, stated on a drawing with a symbol, a tolerance value and referenced datums.

The system is the quantity of matter or region chosen for study, while the surroundings are everything outside it; the boundary between them may be fixed or movable.

Energy is conserved: the heat added to a closed system equals the increase in its internal energy plus the work done by the system on its surroundings.

A combined property equal to internal energy plus the product of pressure and volume, convenient for analysing flow processes and heat exchange at constant pressure.

A statement that spontaneous processes have a direction: entropy of an isolated system never decreases, so heat cannot flow unaided from cold to hot.

A material property measuring the rate at which heat conducts through unit thickness for unit area and unit temperature difference, expressed in watts per metre kelvin.

A coefficient relating surface heat flux to the temperature difference between a solid surface and the adjacent fluid, combining the effects of conduction and fluid motion.

A statement of mass conservation for steady flow, requiring that the product of density, cross-sectional area and velocity stays constant along a stream tube.

An energy relation for steady, incompressible, frictionless flow along a streamline, stating that pressure head, velocity head and elevation head sum to a constant.

The condition under which a scale model and its prototype behave similarly, requiring geometric, kinematic and dynamic similarity, usually achieved by matching dimensionless groups.

A dimensionless or dimensional index describing pump or turbine geometry, defined from speed, flow rate and head, used to select the correct machine type for a duty.

The formation and collapse of vapour bubbles in a liquid where local pressure falls below vapour pressure, causing noise, loss of performance and erosion of metal surfaces.

Stress is internal force per unit area, while strain is the fractional deformation produced; their ratio in the elastic range gives the modulus of elasticity.

The negative ratio of lateral strain to longitudinal strain in a loaded member, a material constant typically near one third for metals.

The normal stress acting on a plane where shear stress is zero, found from the stress transformation equations or Mohr circle construction.

A graphical construction plotting normal stress against shear stress for all plane orientations, giving principal stresses, maximum shear and their directions.

Progressive fracture of a part under repeated or fluctuating loads at stress levels below the static strength, often starting at a stress concentration.

Localised increase in stress near abrupt changes in section, holes or notches, quantified by a factor applied to the nominal stress.

The stress amplitude below which a material survives an indefinitely large number of load cycles without fatigue failure, characteristic of steels.

The property that any part of a given type can replace another without hand fitting, achieved by controlling dimensions within specified tolerances.

A manufacturing route in which molten metal fills a mould cavity and solidifies, allowing complex shapes; shrinkage and porosity are its main defects.

A permanent joining process that coalesces materials by heat, pressure or both, with or without filler metal, producing a heat-affected zone alongside the joint.

The relative ease with which a material can be cut, judged by tool life, cutting forces, surface finish and chip form under given cutting conditions.

An empirical relation between cutting speed and tool life of the form speed times life to a power equals a constant, used to select economic cutting conditions.

A cost technique comparing fixed and variable costs with revenue to find the output at which total cost equals total revenue and profit begins.

The systematic examination of method and time in a production system, combining method study to improve work and work measurement to set standard times.

The cosine of the phase angle between voltage and current in an alternating circuit, indicating the fraction of apparent power that performs useful work.

An alternating supply of three voltages equal in magnitude and 120 electrical degrees apart, delivering constant power and enabling efficient motor operation.

An algorithm is a finite ordered set of steps solving a problem; a flowchart shows the same logic pictorially using standard symbols for decisions and processes.

A program construct that repeats a block of statements while a condition holds or for a counted number of times, avoiding duplicated code.