Grade 8 Technology Comprehensive Review

Vocabulary practice flashcards covering structures, mechanical systems (gears, cams, levers), electricity, engineering graphics, packaging materials, and energy usage from Grade 8 Technology notes.

Frame Structure

A structure made up of different bars (members) joined together to form a framework.

Member

An individual bar or part that is joined with others to form a framework.

Roof Truss

A structural framework used in most houses and buildings to support the weight of roof timbers and roof coverings.

Strut

A structural member that forms part of a frame and is designed to resist compression force.

Tie

A structural member that holds or pulls together two other members to resist tension.

Rafter

A series of inclined parallel beams that form part of a roof structure to support the coverings.

Tie Beam

A horizontal beam that connects two opposite rafters together to complete a roof truss.

Shear Force

A force that acts by sliding one part of a structure past another part in opposite directions.

Torsion Force

A twisting force that turns a member in two different opposing rotational directions.

Tension Force

A pulling force that stretches or pulls a member apart.

Compression Force

A pushing or squeezing force that presses against a structural member.

Electrical Pylons

Huge frame structures that span vast distances and are designed to support heavy overhead electrical cables.

Cross-bracing

A method where a frame structure is stiffened and stabilized by diagonal members that cross one another.

Triangulation

The arrangement of members into triangular shapes to brace and provide rigidity to a frame structure.

Beam

A horizontal length of steel or concrete supported at both ends that resists bending under load.

Girder

A large main beam used in heavy construction to support other secondary beams and loads.

Lintel

A horizontal structural beam installed across the top of an opening (such as a door or window) to provide support.

Column

A vertical member of a structural frame that carries compressive loads downwards to the foundation.

Fracture

A type of structural failure that occurs when an object cracks or breaks because excessive pressure is applied.

Bending (Structural Failure)

A structural failure that occurs when a member begins to curve due to a downward force applied from above.

Toppling Over

A structural failure that occurs when a structure falls over because it is unstable.

Reinforced Concrete

Concrete that has steel rods, bars, or mesh embedded inside to withstand tension alongside its natural compression strength.

Plywood

A manufactured wood board made of thin layers glued together with alternating grain directions, always made with an odd number of layers.

Cam Mechanism

A mechanism consisting of an axle (camshaft), a rotating cam, a guide, and a follower, designed to convert rotary motion into reciprocating motion.

Follower

A stiff rod in a cam mechanism that rests on the cam and moves straight up and down or back and forth.

Eccentric Wheel

A circular cam with an off-centre axle that causes the follower to move with a gentle, wavelike motion.

Snail Cam

A snail-shaped cam that rotates in only one direction, causing a steady rise and an abrupt drop.

Crank

A mechanism used to convert rotary motion into reciprocating motion, functioning as an adaptation of a second-class lever.

Gear

A wheel with evenly spaced teeth around its edge designed to mesh with another toothed wheel.

Driver Gear

The input gear attached to the power source or input axle that causes the system to move.

Driven Gear

The output gear that receives motion and force from the driver gear.

Mesh

To link together or engage the teeth of one gear with the teeth of another gear.

Counter-rotation

The phenomenon where two meshed gears rotate in opposite directions to each other.

Idler Gear

A gear wheel placed between two larger gears that synchronises their direction of rotation without altering the overall speed ratio.

Gear Train

A connected chain or system of several gears used to transmit rotary motion from one shaft to another.

Gear Ratio (GR)

The ratio calculated as $\text{Gear Ratio} = \frac{\text{Number of Teeth on Driven Gear}}{\text{Number of Teeth on Driver Gear}}$ or $\frac{\text{Diameter of Driven Gear}}{\text{Diameter of Driver Gear}}$.

Velocity Ratio (Gears)

The ratio calculated as $\text{Velocity Ratio} = \frac{\text{Velocity (rpm) of Output Gear}}{\text{Velocity (rpm) of Input Gear}}$ or $\frac{\text{Number of Teeth on Driver Gear}}{\text{Number of Teeth on Driven Gear}}$.

Force Ratio (Gears)

The ratio determining output turning force compared to input turning force, calculated as $\frac{\text{Number of Teeth on Driven Gear}}{\text{Number of Teeth on Driver Gear}}$.

Trade-off (Mechanisms)

The mechanical rule stating that speed and force cannot increase simultaneously: gaining more force results in less speed.

Spur Gear

The most common type of gear with parallel teeth, used in devices like washing machines, bicycles, and watches.

Bevel Gear

A gear with angled teeth that changes the axis of rotational motion through an angle of $90^\circ$, used in dentist drills and electric typewriters.

Rack and Pinion

A mechanism comprising a round gear (pinion) and a flat toothed rail (rack) that converts rotary motion into linear motion.

Worm Gear

A gear system consisting of a threaded screw meshing with a gear wheel that provides strong turning forces, found in corkscrews and guitar tuners.

Single Lever

A simple rigid beam that rotates around a fixed point of support called a fulcrum to multiply force.

Effort Arm

The distance along a lever measured from the fulcrum to the point where the input effort is applied.

Load Arm

The distance along a lever measured from the fulcrum to the point where the output load is situated.

Mechanical Advantage (Levers)

A measure of force multiplication calculated as $\text{MA} = \frac{\text{Length of Effort Arm}}{\text{Length of Load Arm}}$.

First-Class Lever

A lever class where the fulcrum is positioned between the effort and the load, such as in a crowbar (single) or a pair of secateurs (linked).

Second-Class Lever

A lever class where the load is positioned between the fulcrum and the effort, such as in a wheelbarrow (single) or a heavy-duty stapler (linked).

Third-Class Lever

A lever class where the effort is applied between the fulcrum and the load, providing no mechanical advantage ($\text{MA} < 1$) but increasing speed/distance (e.g., broom, tweezers).

Linkage

A mechanism made by connecting two or more levers together to reach over a distance, change direction of movement, or increase movement range.

Inclined Plane

A slanting surface connecting a lower level to a higher level, used to raise or lower a load with reduced effort.

Wedge

A double-inclined plane with two sloping faces that converts a forward or downward force into perpendicular lateral forces to split or push things apart.

Wheel and Axle

A mechanism consisting of a disc or wheel that rotates together with or around a central shaft to move loads easily over a surface.

Work

The energy transfer that occurs when an applied force moves an object across a distance, calculated as $\text{Work} = \text{Force} \times \text{distance}$.

Short Circuit

A fault occurring when two uninsulated current-carrying wires touch, causing current to bypass the normal load, surge, overheat wires, drain batteries, and risk fire.

Bagasse

The dry fibrous cellulose material that remains after all juice is crushed and extracted from sugarcane, utilized as a fibre source in paper making.

Paperboard

A thick, rigid paper-based packaging material manufactured by combining recycled pulp and new virgin pulp.

Corrugated Card

A sturdy, lightweight packaging material constructed from three paper layers: two flat outer linerboards sandwiching a wavy, fluted inner layer.

Biodegradable Human-Made Packaging

Packaging designed to decay naturally into compost without taking up space in landfills or releasing large volumes of toxic gases.

Orthographic Projection

A 2D technical drawing method that shows an object through distinct two-dimensional views: Front View (FV), Top View (TV), and Side View (SV).

Isometric Drawing

A 3D pictorial drawing technique that depicts objects with vertical lines at $90^\circ$ and horizontal receding edges projected at $30^\circ$ to the horizontal baseline.

Master Cog

The input drive gear on a bicycle attached directly to the pedal crank.

Slave Cog

The output driven gear on a bicycle attached to the rear hub and wheel.

Derailleur

A bicycle mechanism that shifts the chain from one sprocket to another to change gear ratios and alter speed or output force.

Rotations Per Minute (RPM)

A measurement of rotational velocity indicating the total number of full revolutions a wheel or shaft completes around its axis in sixty seconds.

Bio-fuels

Fuels derived directly from living or organic plant matter (such as firewood) that poorer households frequently burn for basic heating and cooking.

Illegal Electrical Connections

Unauthorized power lines spliced into mains lines to supply informal dwellings, creating extreme danger and increasing electricity costs for all consumers.