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