Section 3.0 – Structural Strength and Stability

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.

3.1 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

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?

In your textbook - Pg. 309

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

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

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

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

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

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

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!

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)