1. Section 3.0 – Structural Strength and Stability

2. Over the years many materials such as animal skins, mud, and sticks were used. Today designers have a wide variety of materials to choose from which have been discovered or invented.
Today we know which material will be the best for a specific function.

3. 3.1 Materials and their Properties
These are some of the most important properties of materials that help decide if they should be used or not. Each of these properties are a term you must know how to define.
Brittleness – how easily does the material break
Ductility – how easily can the material be made into wire
Hardness – how easily the material can be scratched
Plasticity – how easy is the material to shape
Resistance to heat – how is reacts with heat
Resistance to water - how is reacts with heat
Compression – its ability to be squeezed
Tensile strength – stretch or pulled

4. A materials property is not the only thing that is taking into account, there are other factors as well…
Aesthetics (definition from section 1.0)
Consumer demand – who wants it?
Availability
Cost - $ or $$$$
Effect on the environment
Disposal of waste – can it be recycled? Is it expensive to dispose of?

5. In your textbook - Pg. 309

6. Deformation
Deformation – the change in shape in a structure or any structural component
This happens when the material is unable to resist the load acting on it
When to much deformation has occurred the structure has the possibility of failure

7. Flexibility
Flexibility - is the ability of a material to be bent under force without breaking
This means it can change shape under a load without breaking
Examples: tall building or tree in the wind

8. Section 3.2 – Joining Structural Components
What is a Joint?
A place at which structural parts are joined (can be rigid or fixed for proper function
Examples: Human Knee/Elbow, Arm on a pair of glasses, Hinges on locker or door
What is Friction?
A force that results when two surfaces move/rub against each other
The force of friction depends on roughness or smoothness of the two surfaces that are in contact with one another
Example – moving a desk across the floor vs. moving the desk across the floor with a friend sitting in it

9. Joints that Rely on Friction
1. Nails, Screws, Rivets, Tack, Staples
- friction between the metal and the material that allows for it to be held together
- Screws, tack, and staples have an advantage because they are easily removable
2. Interlocking Pieces
- friction is two surfaces rubbing against each other, therefore by increasing the area you can increase friction and the structure will be securely held together
3. Mass
- friction between the base of an item and the surface below it will keep the item in place
- Example: Pyramids in Egypt

10. Joints that Rely on Bonding
1. Glue, Tape, Cement, Welds
- they bond two surfaces together
What is a Fixed Joint?
It is rigid, it does not move (preventing movement)
Examples: welding, cementing, gluing which results in the parts of the structure being firmly secured
What is a Moveable Joint?
flexible/moveable (parts can move if needed)
Examples: hinges on a door, knees, elbows, shoulders

11. Section 3.3 – Properties of Materials in Plant and Animal Structures
Materials in the Human Structure
Bones, Ligaments, and Cartilage (Frame Structure)
Bones
hard/rigid forming a structural frame which can support and protect the other parts of the body
Ligaments
Attaches bone to bone. Is a flexible connective tissue which allows for movement
Cartilage
- reduces friction providing smooth surfaces for movement, is at the ends of some bones

12. Muscles and Tendons Muscles Moves bones by contracting and relaxing
They are attached to bones by tendons
Tendons
attaches the muscles to the bones (strong/flexible)
Joints
Ball and Socket (shoulder/hip joints)
Hinge (elbows/knees)
Pivot (spinal column)
Gliding (wrists)
all of these joints allow MOVEMENT!

13. Skin (human shell)
Tough, flexible
It protects the inside body from the outside environment (waterproofs the body and protects it from bacteria) and regulates temperature (sweating and shivering)
Materials in a Tree’s Structure
Draw, Label and Explain the 5 layers a tree is composed of, shown in Figure 3.17 (pg.321)