Structures FORM AND FUNCTION This slideshow will guide you to learn about: -What makes a good structure -Form and Function -Different Types of Structure -Forces that Act on Structures -Structural Shapes and Components -Centre of Gravity and Stability -Symmetry -Structural weakness and failure

What is a Structure? SKELETON NEST It’s hard to define what a structure is because just about every object you encounter is a structure. There are so many different types! To begin thinking about structures, read and copy into your notes the explanation under “Why is this important?” on page 97. Read pages 98-99 then complete the organizer with examples of natural and human made structures TRADITIONAL HOUSE GALAXY GEODESIC DOME TREE

FUNCTION AND FORM The FUNCTION of a structure is its purpose i.e. why it exists. For example, a bridge’s function is to span a gap like a river valley. Read and study page 101 and take notes in the organizer in your notes. Copy into your notes: “The FORM of a structure is its shape, size, and the materials it’s built from. The FORM of a structure depends on its function e.g. a house has to have a FORM that will allow people to live in it.” From the previous slide, choose two structures that have different forms but could be used for the same function. Complete the organizer.

SOLID STRUCTURES We can CLASSIFY structures based on their form, into SOLID, FRAME, AND SHELL structures. First, SOLID STRUCTURES. Read the paragraph on page 102 and complete the organizer in your notes. Answer this question: Even though it has door holes in it, why is the sand castle still a solid structure?

FRAME STRUCTURES Now FRAME STRUCTURES. Read the paragraph on page 102-103 and complete the organizer in your notes. Answer the question: Describe two advantages that frame structures have over solid structures.

SHELL STRUCTURES An finally (almost)…SHELL STRUCTURES. Read the paragraph on page 103 and complete the organizer in your notes. Answer the question: Why do all liquid containers have to be shell structures?

COMBINATION STRUCTURES I said “almost”…Structures can also be a combination of two or more of the other types. Then they are called COMBINATION STRUCTURES. Read the paragraph on page 104 and complete the organizer in your notes. Answer the question: What types of structures are combined to make the play structure on this slide?

FORCES ACTING ON A STRUCTURE Read page 108 and take notes to understand the basics about forces acting on structures. DESCRIBING FORCES It’s important to understand the following terms about how forces act on a structure: -Magnitude (strength) of the force -Direction of the force (where it comes from) -Point and Plane of Application (where the force meets the structure) From page 110, copy the chart into your notes to learn the terms.

EXTERNAL FORCES An EXTERNAL FORCE on a structure comes from outside the structure. An external force could be a strong wind blowing against a bridge, or someone pulling on a drawer. Read page 109 and then pages 110-111 and define the following terms: -external force -gravity -load -static load -dynamic load Sketch the bridge diagram to help you understand these terms.

The Tacoma Narrows Bridge: INTERNAL FORCES The INTERNAL FORCES acting on a structure come from within the structure itself when an external force is applied to it. The four types of internal force are: Compression: a force that squeezes or presses something together Tension: a force that stretches apart Shear: a force that pushes in opposite directions Torsion: a force that twists To learn these forces, copy the diagrams on page 112. Engineers, architects, and designers, have to design structures in a way that they can resist all the external and internal forces that might affect them. The Tacoma Narrows Bridge: Strong winds (external force) caused this bridge to start twisting violently. The torsion (internal force) ripped the bridge apart. The bridge designers had failed to account for strong winds and extreme torsion.

STRUCTURAL SHAPES AND COMPONENTS Most people know that a triangle is a stronger structural shape than a rectangle. If you build a structure that combines rectangles and triangles, the structure will be even stronger. Read page 131 to review this idea. Engineers use strong shapes in various STRUCTURAL COMPONENTS which can help increase the STRUCTURAL STRENGTH of a structure. Create diagrams of 4 of the structural components on page 132.

CENTRE OF GRAVITY and STABILITY HIGH CHAIR “A” Have you ever sat on a wobbly chair or stool. It might be unstable because the designer didn’t get the centre of gravity correct. Read page 133 and 134, to learn what centre of gravity and stability mean. Generally, structures with a lower centre of gravity are more stable. Answer the question: Which high chair do you think would be most stable? Explain your answer by comparing the designs and use the term centre of gravity in your answer. Answer the question: The front end of a car is designed to be weak and unstable…Why do you think this is the case? HIGH CHAIR “B”

SYMMETRY Read the text about SYMMETRY on page 143. Two reasons are given for why many structures are symmetrical. Explain the reasons in your notes. Answer the question: Think of your house. Is it perfectly symmetrical? Why not? Remember that the form of a structure depends on its function. Symmetry is often used because it makes sense for the function of the structure. This is true for a tennis racquet (symmetrical) and a hockey stick (asymmetrical)

WHEN THINGS GO WRONG A structure may not be able to withstand all the forces that it has to face if it is poorly designed or built. To understand what happens as a structure weakens, we use the following terms. Read about them on page 135 and complete the organizer. -Structural Stress -Structural Fatigue -Structural Failure

FAIL! As you saw with the bridge collapse from a previous slide, structures can fail if they are not designed properly, leading to structural failure. Here are some reasons why a structure might fail: -structure not strong enough to resist external forces -structure not strong enough to resist internal forces -structural shapes used are inappropriate to the function of the structure -the structure has been weakened by age or exposure to external forces -the materials used were too weak Look at the picture of the chair collapse. Write a paragraph explaining why you think this structure may have failed. Try to use the terms you have learned.

READY TO BUILD You’ve learned many of the concepts related to what makes a good structure. You are almost ready to design and build. In your notes make a list of any other factors, that you haven’t yet studied, that might help to make a good structure.