Topic 1: Mass & Force Mass & Weight

Mass is the total __________________ in an object

Weight is the force of ________________on an object

The mass of an elephant on the moon is the same as if he is on earth

There is less gravity on the moon, so he has less weight

If he were on Jupiter, his mass would still be the same but his weight would be

way higher!

Mass

Mass is the total amount of matter in an object

Units of mass follow the Primary ___________________of Mass, the kilogram

Mass is measured using a ________________________________

The object is put on the balance and mass is added until it is balanced out.

Weight

All objects with mass have __________________

Sir Isaac Newton was the first to describe gravity

The amount of ___________________ in objects and the ________________ between objects determines the amount of gravity

Weight is determined by the amount of gravity acting on an object

A Newton (N) is the unit of force – including the downward pull of gravity

Weight can be measured with spring scales or force meters in Newtons.

Forces

Forces are __________ or ____________ acting on objects

Force diagrams are a simple way of showing the forces on an object

Direction of force must always be shown

Draw another force diagram for an object of your choice:

Triple Beam Balances & Force Meters

Fill out the table below with the measurements of three objects in the classroom.

Object Mass (units) Weight (units)

Topic 2: Types of Structures ___________________ are things with a definite shape and size, serving a particular

function

To perform a ___________________ a structure must resist forces

▪ Such as pushes or pulls

▪ These forces may change the shape or size

Natural Structures Manufactured Structures

Not made by people May be biotic or abiotic

Manmade Often based on nature

Examples: Examples:

Types of Structures - Mass

A mass structure is made of

similar materials piled together

List some examples of mass

structures:

Mass structures use a lot of ___________________

The weight of the materials makes the structure _________________

Small spots of wear or breaking seldom make a difference overall

Not all mass structures are completely solid

Mass structures must be very _______________ designed because of size and weight

Mass structures may _________ because:

It may not be heavy enough to stay

in place

It is too thin, or poorly fastened and

parts may push out of place

It may be so heavy it sinks or leans

It may not be _______________ to the ground well enough

Types of Structures – Frame

Structures made of a strong skeleton

Some frames are covered, depending on the

function

List some examples of frame structures:

Frame structures are relatively _______________ to

design and build

Often _______________ expensive designs to build

Frame structures often need to be

_______________

Complicated designs need to be very exact

Small errors in building a frames structure can

cause major damage

Types of Structures - Shell

Shell structures are typically ___________and _______________

List some examples:

They keep their _____________ and support loads without a

frame or solid mass inside

Some are __________ like egg shells, others are flexible like

parachutes

They make great containers

They use minimal building materials

Tiny weaknesses, like scratches can cause failure

Uneven drying/cooling of building materials may cause

____________________

Construction is often slower and more difficult than other

structures

Topic 3: Describing StructuresDesigning Structures

Designers need to consider 4 main parts for a ___________________ structure:

Function

__________________

Safety

Cost : Materials &Environmental Impact

Function

What does a structure do?

Contain, transport, shelter, support, lift, fasten, separate, communicate, break,

hold

Loads are forces (weight) a structure resists

________________ loads change

_________________ loads stay the same

Aesthetics

_________________ is the study of beauty in art and nature – does it look good?

‘Beauty is in the eye of the beholder’

Safety

Safety very important to ____________________

Better safe than sorry is the basis of a margin of

___________________.

Extra strength in case of failure - Many roofs in Canada have a

margin of safety for snow load!

Cost is sometimes challenging to _______________________ with

safety

Not all safety concerns can be foreseen!

Cost

The properties of a material must serve the _________________ of a structure.

Materials – Composites

Composites combine multiple ________________________

They bring together strengths of materials and balance weaknesses

Materials – Layered

Layers of a material are called __________________

Often, layers will be put together in a particular way to balance weaknesses

What are some layered structures?

Materials – Woven & Knit

Woven or knit materials are made up of linked threads which distribute

_______________________ through the whole structure

They offer _____________________ and can be layered

Cotton clothing, rugs, netting, screens

Sketch the texture of three woven materials below:

Materials – Flexibility

Pressed or melted substances can also offer ____________________

Plastic wrap, aluminum foil, felt, paper

Flexible materials are great for structures that need to be folded, ______________ or

molded

If they are lightweight it can make transport, storing, and use more convenient

Tents, parachutes, clothing

Material Choice

Consider: Cost, Appearance, Environmental Impact, Energy efficiency

Design – Joints

Materials often need to be connected, joints are typically weak points

Mobile joints – allow movement

Door hinges, elbows, ___________________

Rigid joints – are locked in place

Dovetail joints, rivets, nails, _____________________

Fasteners: Nails, staples, bolts, screws, rivets, dowels

Interlocking ________________: Folded seams, dovetails, puzzles, Lego, zippers

Ties: Thread, string, rope: shoes, drawstrings

Adhesives : ____________________ (hot glue guns), solvent based (crazy glue), epoxies

- stronger bond = stronger chemicals

Melted bonds: Welds, soldering

Topic 4: Forces, Loads & StressesForces

External forces are stresses that act on a structure from outside

Weight of a car, wind blowing, snow; live loads

They cause internal forces – stresses within the materials of the structure

Internal stresses can change the shape or size of a structure this is called deformation.

Deformations can be repairable or cause a structure to fail

External Forces – Loads

A dead load is a permanent force, acting on a structure.

This includes the weight of the structure itself.

A live load is changing, or non-permanent force acting on a structure.

This includes the force of the wind ,the weight of objects on a structure

Impact forces (collisions with the structure) are another type of live load.

Internal Forces

______________________ forces stretch a material by pulling its ends apart

Tensile strength measures the largest tension force the material can resist before failing.

______________________ Forces crush a material by squeezing it together.

Compressive strength measures the largest compression force the material can resist before it loses its shape or fails.

_____ forces bend or tear a material by pressing different parts in opposite directions at the same time

Shear strength measures the largest shear force the material can resist before it rips or fails

___________________ Forces twist a material by turning the ends in opposite directions.

Torsion strength measures the largest torsion force the material can withstand and still spring back into its original shape.

A ____________________ force is a combination of tension and compression

Label the demonstrated stresses in the image below:

Topics 5 & 6: How Structures Fail & Designing with Forces

Designing with Forces

Designers often consider:

Load _______________

Directing forces to help the structure

Shaping parts to _________________ forces the structure will have to resist

Problem: Rectangular frames are easiest to build BUT Load forces can easily deform them by pushing or pulling them apart

Consider Triangles

Triangles are _______________shapes

Triangles do not collapse as easily as

rectangles and are used in trusses

Frame structures have many vertical posts

to share the load

No single part carries the load

Problem: Many load bearing structures have a horizontal span supported only at the ends. The forces exerted on the middle causes the bending that directs forces outward to vertical beams. Sometimes more vertical beams in the middle are not practical.

Consider Arches

Arches can be made of shaped stones

The centre stone is called the ________________

As the force of the keystone is pushed against those next to it they push on those

next to them ____________________ the force out and down.

Domes and shell structures as well as framed arches use the same ________ distribution

Consider a Cantilever

A Cantilever is a horizontal span supported at one end by ___________________

Double _______________ bridges are very strong

The beams from the top of the

columns pull ______ on the ends

The beams on the bottom push

upward on the ______________

Consider Suspension

Suspension bridges work similar to cantilevers

redistributed forces are directed to columns.

Tension is brought up the ______________

cables to the horizontal

The horizontal cables exert balanced

_________________ on the columns

Consider Braces

Braces can be added and materials _________________ to direct forces outward

through solid parts of a structure to the ground.

Problem: Large Solid Beams are very strong, but lots of material means lots of weight and cost

Consider Hollow Structures

Shell and frame structured beams can be very strong and comparably _____________

Box _____________ I-beams, T-beams and L-beams are very ______________and are

considerably less material, and cost.

Corrugations are _______________ of thin material

between layers

They maintain strength while lightening

weight and reducing materials

Many hollow wooden doors have

_______________ like cardboard.

Most Bones are _______________ and have a light, spongy layer inside

They are strong but light structures

Problem: Very tall structures can be very beautiful, but with hollow insides for multiple stories, the walls are likely to fall out or in and collapse

Consider Flying Buttresses

Flying buttresses are like training wheels for ___________________

They redistribute the forces of the walls and push them __________ toward the ground

Many gothic _______________ use them to support their towering walls

Friction

______________is when there is a force resisting movement

Friction can be used to strengthen structures

Screws, bricks, fence posts and flag poles use friction to better serve their function

Failing Structures

Structures can _________________ when stresses are so strong, the structure cannot resist by:

Snapping, Twisting, Buckling, Bending , Shearing

Torsion – Twisting

_________________ forces on materials, especially brittle ones, can cause shearing in the material

Torsion forces cause materials to twist and tangle but not always break

Buckling

Bending or buckling failure is when _________________ strength fails

The material gives way to forces it can no longer resist often causing ___________________ and bending deformations

Metal Fatigue

With constant or repetitive bending or __________________metal weakens

These actions change the arrangement of the particles

This causes small ________________ and weaknesses

Shear

This is when small cracks or _______________ cause the material to fail

One section may slide over another along a weakness

A building may slip sideways

Using Structural Failure

Boat motors are designed to break under

shear force when tangled

Twisted strands create yarn – they are twisted

just enough for strength and flexibility

Preventing Failures

Triangles in Frames: triangles are excellent at redistributing weight evenly.

________________: redistribute weight of load pushes weight down and from the keystone over the stones to the ground.

Cantilever and _______________: A cantilever uses a horizontal span supported at one end by column.

Suspensions use the tension in cables to redistribute the load onto columns.

Hollow Materials: Use of strong hollow materials can decrease the weight of a building/structure.

_________________: Use building material that encourages friction – rubbing materials against each other

Topic 7 – Stable Structures

Introduction

A structure is likely to fail if forces are ____________________

Engineers need to think of many factors to make sure a structure will be stable.

Center of Gravity

_______________________________ is the point where all of the mass of the structure is evenly distributed around

Engineers need to know center of gravity to stabilize a structure

The force of gravity acts on ________ parts of the structure, _______the time

If all parts are evenly distributed around the center of gravity, then the structure will be stable.

Counterweights

Counterweights are used in a structure to_____________ the center of gravity to regain stability

Knowing the center of gravity can identify if the structure is stable or unbalanced.

Foundations

The foundation of a structure is _______________ the base

It must be stable or compression may cause _________________

Structures with_________________ foundations may crack and shift

Moisture, consistency, and disturbance must be considered

Foundations are very secure on sold _______________

Foundations may need pilings

________________________ can be used, if the layers of soil above the bedrock

are loose enough.

large metal, concrete or wood cylinders go

into the______________ to bedrock

Footings

It may be hard to reach the bed rock with

________________ so houses &decks are often

built with footings instead of pilings.

Spin Stabilization

When an object spins, it gains

angular _____________________

Angular momentum means it wants

to stay at the same

______________; it becomes harder

for gravity to pull over

Objects stabilized but spin are called

________________________

Gyroscopes, which use ____________________, have a number of uses including:

Boats, Rockets, Satellites, Footballs

Gyroscope built into a ship to prevent unwanted movement