Grade 8 Technology Lecture Notes: Structures and Mechanisms

Flashcards covering Grade 8 Technology topics including graphic conventions, technical drawing standards, mechanical forces, structural members, bridge types, simple machines (lever, wedge, gear ratios), and environmental impact of materials.

What is the function of Outlines (Visible Lines) in engineering drawings?

Thin, dark lines that establish the real visible borders and geometry of the object to isolate what an observer can see from a given vantage point.

How are Hidden Detail Lines specifically constructed according to standards?

They are dashed lines consisting of uniform $3\,mm$ dashes spaced precisely $2\,mm$ apart.

What geometry do Centre Lines denote in technical drawings?

Axes of symmetry, central midpoints of circles, and cylindrical geometry.

In technical dimensioning, where should the numeric values be placed on the line?

Numbers must be centered and written directly ABOVE unbroken, light dimension lines terminated by narrow arrowheads.

What symbol is used as a prefix for circle diameter specifications?

The special diameter prefix symbol $\emptyset$ (e.g., $\emptyset30$).

What does a Scale $1:2$ represent in technical drawing?

A reduced scale used for large constructions where the drawn image is exactly half the item's size.

Define Compression Force.

A pushing, squashing force directed inwards against a structural member, striving to condense its length.

What is Shear Force?

A sliding force that pushes parallel structural elements in opposing directions, forcing internal structures to slide past one another along a plane.

In a frame structure, what is the difference between a Strut and a Tie?

A Strut is a rigid member positioned to resist compression forces, while a Tie is a member engineered to resist tension by holding parts together.

What is Triangulation in structural engineering?

Arranging structural members into interlocking triangles to provide exceptional rigidity, as triangles cannot change shape without changing the length of their sides.

How do Arch Bridges handle downward gravity loads?

They transfer downward gravity loads along the curve into compression forces, locking the components tightly together against their foundations.

What is the primary characteristic of an Inclined Plane?

It is the simplest machine with NO moving parts; it uses a ramp to move objects using less force over a longer distance.

According to the transcript, who designed the Hippo Water Roller?

Petzer and Jonker.

What is counter-rotation in meshed spur gears?

When two spur gears mesh together, they always turn in OPPOSITE directions to each other.

State the formula for Velocity Ratio in gears.

$$\text{Velocity Ratio} = \frac{\text{Number of teeth on DRIVER gear}}{\text{Number of teeth on DRIVEN gear}}$$

State the formula for Force Ratio (Mechanical Advantage) in gears.

$$\text{Force Ratio} = \frac{\text{Number of teeth on DRIVEN gear}}{\text{Number of teeth on DRIVER gear}}$$

What is the function of an Idler Gear?

A gear placed BETWEEN two other gears to synchronize them so they turn in the SAME direction.

Define Biodegradability.

The ability of a material to be broken down naturally by air, water, and bacteria into tiny parts that are reabsorbed safely by the Earth.

What renewable resource does the company Green Home use for its biodegradable packaging?

Cornstarch.

What was the South African government's legislative solution in 2003 to combat plastic bag litter?

They banned bags thinner than $30\,\text{microns}$, required consumers to pay for bags, and introduced a special plastic tax to fund recycling.