Engineering EA

Bicycle Function and Purpose

Function: Converts the rider's pedalling force into rotational motion of the wheels using gears, chain, and sprockets.

Purpose: To transport a person efficiently while reducing the effort needed to travel.

Crowbar Function and Purpose

Function: Acts as a first class lever to multiply the applied force.

Purpose: To pry, lift, or remove heavy objects with less effort than lifting them directly.

Car Jack Function and Purpose

Function: Uses a screw mechanism or hydraulic system to multiply force and raise a vehicle vertically.

Purpose: To lift a vehicle so maintenance tasks such as changing a tyre or performing repairs can be carried out safely.

Four types of motion

Linear, rotary, reciprocating, oscillating

Linear Motion

Motion in a straight line where all parts of an object move the same distance in the same direction.

Examples: Elevator, conveyer belt, piston rod

Rotary Motion

Motion in which an object turns about a fixed axis or pivot point.

Examples: Bicycle wheel, gears, fan blades

Reciprocating Motion

Repeated back-and-forth motion in a straight line.

Engine piston, sewing machine needle

Oscillating Motion

Repeated back-and-forth motion about a fixed pivot or equilibrium position, moving through an arc.

Examples: Pendulum, windscreen wiper, playground swing

Inclined Plane

A flat, sloping surface that reduces the force needed to raise or lower a load by increasing the distance over which the force is applied.

Screw

An inclined plane wrapped around a cylinder that converts rotational motion into linear motion and provides mechanical advantage for fastening or lifting.

First-class lever

A lever where the fulcrum is between the effort and the load.

Example: Seesaw

Second-class lever

A lever where the load is between the fulcrum and the effort, increasing force.

Example: Wheelbarrow

Third-class lever

A lever where the effort is between the fulcrum and the load, increasing speed and distance rather than force.

Example: Tweezers

Fixed pulley

A pulley fixed in place that changes the direction of the applied force but does not significantly reduce the effort required.

Movable pulley

A pulley attached to the load that reduces the effort needed to lift the load by increasing mechanical advantage.

Flat belt drive

A system that uses a flat belt to transmit rotary motion and power between a driver pulley and a driven pulley, suitable for higher speeds and longer distances.

V-belt drive

A system that uses a V-shaped belt running in grooved pulleys to transmit rotary motion with improved grip, reducing slipping and allowing greater power transmission.

Spur gear

A gear with straight teeth that transmits rotary motion and torque between parallel shafts.

Worm gear

A gear system consisting of a screw-like worm and a worm wheel that transmits motion between perpendicular shafts, providing high torque reduction.

Rack and pinion

A gear system where a circular pinion gear meshes with a straight rack to convert rotary motion into linear motion, or vice versa.

Mechanical Advantage Formula

Load/Effort

Velocity Ratio Formula

Distance moved by effort/Distance moved by load

Velocity Ratio of Screws

Circumference/Pitch

Velocity Ratio of Pulleys

Number of ropes supporting the load

Velocity Ratio of Belts

Radius, Diameter, Circumference of Driven/Radius, Diameter Circumference of Driver

OR

Driver speed/Driven speed

Velocity Ratio for Gears

Radius, Diameter, Circumference, Number of Teeth on Driven/Radius, Diameter, Circumference, Number of Teeth on Driver

OR

Angular movement of Driver/Angular movement of Driven

Efficiency Formula

(MA/VR)*100

Friction

A force that opposes the relative motion, or attempted motion, between two surfaces in contact.

Static friction

The frictional force that prevents an object from starting to move. It acts on objects at rest and increases up to a maximum value.

Kinetic (sliding) friction

The frictional force that opposes motion between two surfaces that are already sliding past each other.

Coefficient of friction (μ)

A dimensionless value that represents the amount of friction between two surfaces.

Angle of repose (θ)

The maximum angle of an inclined plane at which an object remains at rest before it begins to slide.

AND gate

Produces a TRUE output only when all inputs are TRUE.

OR gate

Produces a TRUE output when at least one input is TRUE.

NOT gate

Produces the opposite of the input (inverts the input).

NAND gate

Produces the opposite of an AND gate; the output is FALSE only when all inputs are TRUE.

NOR gate

Produces the opposite of an OR gate; the output is TRUE only when all inputs are FALSE.

XOR (Exclusive OR) gate

Produces a TRUE output only when the inputs are different (for two inputs, one TRUE and one FALSE).

Logical TRUE (1)

A logic state representing ON, HIGH, or TRUE.

Logical FALSE (0)

A logic state representing OFF, LOW, or FALSE.

Logical identity

A logic operation that leaves the input unchanged (e.g. A=A)

Logical negation

A logic operation that inverts the input, changing TRUE to FALSE and FALSE to TRUE (NOT).

Phase diagram

A graph showing the phases present in an alloy at different temperatures and compositions under thermal equilibrium.

Binary alloy

An alloy made from two elements.

Liquid phase (L)

A phase in which the alloy is completely molten.

Solid phase (α or β)

A solid solution phase with a uniform crystal structure and composition.

Single-phase region

A region of the phase diagram where only one phase exists.

Two-phase region

A region where two phases coexist in equilibrium.

Liquidus line

The boundary above which the alloy is completely liquid.

Solidus line

The boundary below which the alloy is completely solid.

Solvus line

The boundary separating a single solid solution from two solid phases.

Eutectic reaction

A reaction where a liquid transforms into two solid phases simultaneously at a specific temperature and composition.

Eutectic composition

The alloy composition at which the eutectic reaction occurs

Eutectic temperature

The lowest melting temperature of the alloy system, 183°C for the lead–tin system.

Hypoeutectic alloy

An alloy containing less tin than the eutectic composition

Hypereutectic alloy

An alloy containing more tin than the eutectic composition

α (alpha) phase

A lead-rich solid solution containing a small amount of dissolved tin.

β (beta) phase

A tin-rich solid solution containing a small amount of dissolved lead.

Steel

An iron–carbon alloy containing approximately 2.1 wt% carbon or less.

Eutectoid reaction

A reaction where one solid phase transforms into two different solid phases at a specific temperature and composition.

Eutectoid composition

Approximately 0.76 wt% carbon, where austenite transforms into pearlite.

Eutectoid temperature

Approximately 727°C, where the eutectoid reaction occurs.

Austenite (γ)

A face-centred cubic (FCC) solid solution of carbon in iron that exists at high temperatures.

Ferrite (α)

A body-centred cubic (BCC) iron phase with very low carbon solubility; soft and ductile.

Cementite (Fe₃C)

A hard, brittle iron carbide compound containing 6.67 wt% carbon.

Pearlite

A lamellar microstructure consisting of alternating layers of ferrite and cementite formed during the eutectoid reaction.

Hypoeutectoid steel

Steel containing less than 0.76 wt% carbon, consisting mainly of ferrite and pearlite after cooling.

Eutectoid steel

Steel containing 0.76 wt% carbon, consisting entirely of pearlite after cooling.

Hypereutectoid steel

Steel containing more than 0.76 wt% but less than 2.1 wt% carbon, consisting mainly of pearlite and cementite after cooling.

Plain-carbon steel

Steel whose properties are determined primarily by its carbon content, with few or no significant alloying elements.

Low-carbon steel (0.07–0.30% C)

Soft, ductile and easily formed or welded steel with relatively low strength.

Used for: automobile body parts, wire products, structural plates and sections, seamless tubes and boiler plate

Medium-carbon steel (0.30–0.60% C)

Steel with a balance of strength, hardness and ductility, suitable for structural and mechanical components.

Used for: automotive components, including shafts, axles, gears and crankshafts, stampings and forgings, train rails, wheels and axles

High-carbon steel (0.60–2.0% C)

Very hard and wear-resistant steel with high strength but reduced ductility and weldability.

Used for: high-strength spring materials and wires, cutting tools, punches, dies and industrial knives.

Property Trends as Carbon Content increases

Hardness: Increases

Strength: Increases

Wear resistance: Increases

Hardenability: Increases

Ductility: Decreases

Toughness: Decreases

Weldability: Decreases

Machinability: Decreases

Hardness

The resistance of a material to indentation, scratching or wear.

Strength

The ability of a material to withstand an applied force without failure.

Ductility

The ability of a material to plastically deform before fracturing.

Toughness

The ability of a material to absorb energy before fracturing.

Wear resistance

The ability of a material to resist surface damage caused by friction or abrasion.

Hardenability

The ability of steel to form hard structures during heat treatment.

Machinability

The ease with which a material can be cut or machined.

Weldability

The ease with which a material can be welded without defects.

Hot working

Plastic deformation of metal above its recrystallisation temperature, producing refined grains without work hardening.

Cold working

Plastic deformation below the recrystallisation temperature, increasing strength and hardness through work hardening.

Rolling

A metal-forming process in which material passes between rotating rollers to reduce thickness or change shape.

Forging

A process that shapes metal by compressive forces, improving grain flow and mechanical properties.

Work hardening

An increase in strength and hardness caused by plastic deformation during cold working.

Annealing

A heat treatment that softens steel, relieves internal stresses and improves ductility.

Full annealing

Heating steel above the critical temperature followed by slow furnace cooling to produce a soft, coarse-grained structure.

Process annealing

Heating cold worked low-carbon steel below the critical temperature to remove work hardening and restore ductility.

Normalising

Heating steel above the critical temperature and cooling it in still air to refine the grain structure and improve strength and toughness.

Grain

A crystal within a metal with a uniform atomic arrangement.

Fine-grained structure

Small grains that generally increase strength and toughness.

Coarse-grained structure

Large grains that generally reduce strength but improve ductility.

Hardening

Heating steel above the critical temperature followed by rapid cooling to produce a hard martensitic structure.

Quenching

Rapid cooling of heated steel to increase hardness.

Water quenching

Quenching in water, producing the fastest cooling rate and highest hardness but greatest risk of cracking.

Oil quenching

Quenching in oil, providing a slower cooling rate than water and reducing distortion and cracking.

Air cooling

Cooling in still air, producing slower cooling and lower hardness than quenching.

Furnace cooling

Very slow cooling inside a furnace, producing the softest structure.