UNIT 4 Structures & Forces

UNIT 4 Topic 1

Types of Structures

WHAT IS A STRUCTURE?

Structure Something with a definite shape and size which

serves a definite function or purpose

WHAT IS A NATURAL STRUCTURE?

Natural Structure Something that is not man made Follows the same definition of a structure

WHAT IS A MANUFACTURED STRUCTURE?

Manufactured Structure Something that is created by man Follows the same definition of a structure

WHAT IS A MASS STRUCTURE

A structure made by piling up, or forming, similar materials into a particular shape or design – can be natural

Follows the same definition of a structure

HOW CAN A MASS STRUCTURE FAIL?

There are 4 ways a mass structure can fail … Let’s use a sandbag wall for example!

1) The wall is not heavy enough and forces on it push it over

2) The wall could be too heavy, move the earth underneath it, it becomes uneven and topples

3) The wall could be put together poorly resulting in weak links. Certain pieces fall out and wall falls

4) Not anchored to the ground and the external forces will knock it over

WHAT WOULD A LOAD BE?

Load Weight carried or supported by the structure

FRAME STRUCTURES

What is it? A structure with a skeleton like frame Always made of strong materials Can support huge amounts of weight

… if built properly of course!

FRAME STRUCTURES

FRAME STRUCTURES CONT …

All frame structures are not the same Objects such as ladders, snowshoes and

spider webs are only frames That is to say are full of important pieces

More complex objects often attach things to the frame Think a bike … frame is what you sit on and it

supports you but we add… Braking system Steering system Suspension systems Pedals

FRAME STRUCTURES CONT …

Frames can also be hidden … Like in an umbrella or a car

Or exposed (out in the open) Like a drilling rig or bridge

SHELL STRUCTURES Strong and hollow Keep their shape Support loads even without a frame or solid

mass of material inside

SHELL STRUCTURES CONT … 2 Major Benefits of this structure

1) They are completely empty which makes them great containers

2) They are made up a thin layer they use very little building materials

But how does it work?

SHELL STRUCTURES CONT …

SHELL STRUCTURES CONT … So if they are cheaper and very strong – why

don’t we build everything into a dome shape?!

As strong as they are they face many different challenges to be constructed perfectly!

1) Tiny weaknesses cause the whole structure to fail!

SHELL STRUCTURES CONT … 2) If it is formed and constructed out of hot or

moist materials (think clay for example) and dries or cools unevenly you can push or pull in neighboring sections

This causes structural weak points and out of no where it could break!

SHELL STRUCTURES CONT … 3) Think of trying to build a plywood igloo!

Many of our construction materials are not designed for this type of construction

Each piece would need to be shapedindividually

Crazy expensive!

SHELL STRUCTURES CONT … 4) Assembling the finishing materials into a shell

is also very tricky

It needs to be pinned and heldin place in a specificway

Then all the edgesneed special finishing

Crazy expensive again!

MIX & MATCH To make the best of both worlds many

structures in the world mix and match the principles of both designs together Part Frame Structure Part Shell Structure

How does this work?

UNIT 4 Topic 2

Describing Structures

FUNCTIONS

Structures perform a variety of different jobs … here is a list of the most common.

Can you think of a real world example of each?

Containing Transporting Sheltering Lifting Fastening

Separating Communicatin

g Breaking Holding

FUNCTIONS

The first thing all designers/builders think is … “What is this thing supposed to do”

However is it that simple? No way! Structures often have many different functions

What are the functions of a house? What are the functions of a bridge?

FUNCTIONS CONT…

Often, as much as we want the designs to be perfect, when we add multiple functions they are not perfect

Think of a shoe (see pg: 283) What are the functions of a shoe? What happens if we try to water proof a shoe?

AESTHETICS

What are aesthetics? How good it/they look of course!

Aesthetics is actually the study of beauty in art and in nature

Building materials are key in this? Concrete vs. Marble?

Also, remember the KISS principle Keep It Simple Stupid!

SAFETY

Picture an elevator … or look at this! What is the key thing on this panel?

All structures are designed with safetyin mind!

Elevators are designed to hold morethan it could fit for safety

SAFETY Elevators have extra strength that allows it to

withstand much larger loads than it would normally need to carry

Large safety margin! Safe for riders in almost all situations

BALANCE

Making things safer typically means more expensive

Sometimes … builders / designers try to take the easy way out and cheap out – no good!

Also, designs typically take into account events they assume will occur (flood, wind, etc …)

Rare and unexpected events are tough to plan for because there are so many things that could happen!

Oops!

MATERIALS

So … as you have seen there is a lot of thought that goes into designing something.

Once you have a design it is time to determine what type of materials you will use to construct it

Let’s explore the most common categories …

COMPOSITE MATERIALS

There are different kinds of strength… Tension (pulling) Steel rods Compression (pushing) Concrete

To enable the structure to withstand both types of forces acting on it, a composite material is used

Composite is essentially a combination of materials Reinforced concrete 

Concrete poured over steel rebar (rods).

LAYERED MATERIALS

Pressed and glued together

Combining the properties of the different materials.

The layers are often called laminations.

Did you know this about pop cans and canned foods?

WOVEN / KNITTED MATERIAL

Spinning or twisting, looping or knotting fibers together gives material added strength

A loom is used to weave two or more pieces of yarn together in a criss-cross pattern to make cloth

Pressing, gluing, melting and dissolving are also ways to combine materials to gain strength.

CHOOSING MATERIALS

When choosing materials it is about … Weighing advantages vs. Disadvantages

For example… Higher quality

& stronger materials are usually more expensive

So here are the most common factors to consider!

FACTORS TO CONSIDER

Cost Will inexpensive materials allow the structure

to perform its function over a reasonable time?

Appearance Is the appeal of the structure

‘pleasing' over time?

Environmental Impact Does the structure harm the environment

Energy Efficiency Does the structure

conserve energy?

JOINTS

How would you define “Joint”

How do you fasten the structure together?

Are there different kinds of joints?

All this and more on today’s lesson …

JOINTS

TYPES OF JOINTS

Mobile Joints Joints that allow

movement

Rigid Joints Joints that do not allow movement

FASTENING

Fasteners  Devices that hold two, or more, things together Ex: nails, staples, bolts, screws, rivets and

dowels

Unfortunately, the holes made in the structure, by the fastener, actually weaken the structure

One fastener allows movement when the parts are pushed or pulled

More than one will make a more rigid joint - but, will also weaken it more.

INTERLOCKING

Interlocking shapes Fit together because of their shape

Examples

Dovetail joints in drawers, dental fillings, Lego

TIES

Ties Essentially a form of fastening

Examples Thread, string and rope

ADHESIVES

Adhesives Sticky substances can also hold things together. 

Thermosetting glues  hot glue Solvent-based glues  drying glue Strengthen the joint because of the bonds

between the particles Even the strongest adhesives can fail under

extreme conditions … if the joint is stronger than the material it is joining, the material next to the joint can fail.

Adhesives can also be a health hazard

MELTING

Melting  Pieces of metal or plastic can be melted together

Examples Welding, soldering - brazing or using chemicals

UNIT 4 Topic 3

Mass & Force

MASS VS. WEIGHT

So this is the time we learn something very important …

… that is what is mass? … that is what is weight?

Let’s go!

MASS

Think back to the particle theory! All things are made up of particles right?

Can you guess where I am going with this…?

The mass of an object is the measure of the amount of matter in it

The mass is the number of particles the substance has

MASS – UNITS OF MEASURE?

To set the standard … A small cylinder of metal was used by which, to compare different substances.

This standard (in the metric system) is called the primary standard of mass, and the amount of material in it is called one kilogram (kg).

Smaller masses are measured in grams (g). 'Kilo' means one thousand (1000)

and is equal to 1000 grams. Very small masses are measured

in milligrams (mg). 1000 mg. equal 1 g.

MASS – THE STANDARD TO MEASURE

A balance is used to measure the amount of mass in a particular substance

Standard scientific balances include the triple beam balance and the equal arm balance.

MASS – IN SUMMATION

How much would your mass be on Earth compared to the moon?

Trick question it stays the same … the big idea is…

No matter where you are in the universe your mass stays the

same!

FORCES & WEIGHT

Force is a push or pull on an object The standard unit of force is called

a Newton (N) (1 newton of force will stretch a thin rubber

band, or will be what it takes to lift up a D-cell battery)

A force meter (spring scale) is used to measure the amount of force - the pull of gravity - on a mass.

To describe a force accurately, you need to determine its direction and size.

WEIGHT & GRAVITY

Time to play with spring scales!

WEIGHT

Weight is a force and should properly be measured in newtons

Sir Isaac Newton described the force that pulls objects together as the force of gravity

The gravitational forces between two objects depends on the masses of the objects and the distance between them

This gravitational force is called weight Because gravitational force depends on the

distance between two objects, an object's weight changes depending on where it is. (the farther away from the earth, the less the weight.

REMEMBER!!

Mass is the amount of matter an object is made of

Weight is the force with which gravity pulls on an object.