Structures and Forces Lecture Notes

Flashcards covering vocabulary and definitions related to structures, forces, loads, stability, symmetry, and ergonomics as presented in the lecture transcript.

Structure

Any object with a definite size, a definite shape, a purpose, and the ability to support a load.

Solid structure

A structure that is solid all the way through with no hollow space or skeleton, where the mass itself resists the load.

Frame structure

A skeleton of parts joined together that is mostly hollow and gains strength from how the parts are arranged and connected.

Shell structure

A thin curved outer surface enclosing a hollow space where the curved shape provides strength rather than thickness.

Combination structure

A structure that is a mix of two or more types, such as a car consisting of a shell body and a frame chassis.

Force

Any push or pull applied to an object, characterized by magnitude, direction, and point of application.

Magnitude

The strength or size of a force, measured in Newtons ($N$).

Direction

The way a force is applied, such as up, down, left, right, or sideways.

Point of application

The exact location on an object where a force is applied.

Contact forces

Forces that occur only when objects physically touch, such as wind on a wall or a foot on a pedal.

Non-contact forces

Forces that do not require physical touching, such as gravity, magnetic force, and electrostatic force.

Gravity

A non-contact force that pulls toward Earth's centre and which every structure must resist constantly.

Mass

The amount of matter in an object, measured in grams ($g$) or kilograms ($kg$), which stays the same everywhere in the universe.

Weight

The force of gravity pulling down on an object, measured in Newtons ($N$), which changes depending on location.

Spring scale

The tool used to measure weight.

Load

Any force acting on a structure.

Dead load

The permanent weight of the structure itself that never changes, such as the concrete and steel of a bridge.

Live load

The weight of objects or people that a structure supports, which changes over time.

Dynamic load

Forces not caused by gravity that can come from any direction and change rapidly, such as wind, earthquakes, or waves.

Static load

The term for combined dead load and live load, both of which are caused by gravity pulling straight down.

External force

A force applied from outside the structure that creates internal forces inside the material.

Compression

An internal force that involves squeezing or pushing from opposite sides so the material is squished together.

Tension

An internal force that involves stretching or pulling from opposite ends so the material is pulled apart.

Torsion

Twisting forces where a material is being twisted in opposite directions.

Shear

Parallel internal forces pushing in opposite directions on different layers, causing material to be cut or slid apart.

Centre of mass

The point where the mass of an object is evenly balanced in all directions.

Centre of gravity

The point where gravity appears to act on the whole object; it always changes together with the centre of mass.

Base of support

The area beneath a structure that supports it, where a wider base increases stability.

Stability

When a structure maintains its shape and position over time by keeping the centre of gravity inside the base of support.

Tipping point

The moment when the centre of gravity moves outside the base of support, causing the structure to fall.

Line of symmetry

The imaginary line that divides a symmetrical object into two mirror-image halves.

Bilateral symmetry

Also known as line symmetry, where one line divides the object into two identical halves.

Visual symmetry

When a structure looks the same shape on both sides, though the mass may not be evenly distributed.

Asymmetrical

A structure with no line of symmetry.

Aesthetics

The study or quality of how visually attractive or beautiful a structure is.

Ergonomics

The science of designing structures and systems so people can use them comfortably, safely, and efficiently (from the Greek ergon and nomos).

Repetitive strain injury (RSI)

Damage to small muscles of the wrists or hands from constant, repeated activity over a long period.

Universal design

Arranging a structure or device so it is user-friendly for everyone regardless of ability, following five principles: equal, flexible, ergonomic, simple, and safe.

Accessible design

Design features added to meet special needs or targets for people with disabilities, often retrofitted after the original build.