1. Forces and Structures

2. Structure and Forces
How does understanding the effect of forces, properties of building materials, and design characteristics contribute to structural strength and stability?

3. Let’s Review ….Power Teaching
What is a structure?
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What is a structure? Anything with a definite shape, definite size, and definite purpose
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What are the two types of structures?
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What are the two types of structures? Natural and Manufactured
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What is a design?
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What is a design? How a structure is put together, how it is shaped, and the materials that are used to build it
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What are the three designs of structures?
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What are the three designs of structures? Shell, Mass, Frame
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What are the advantages or disadvantages of Mass structures?
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Advantages:
Held in place by its own weight
Doesn’t wear down or break easily
Disadvantages:
Uses a lot of materials
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What are advantages and disadvantages to frame structures?
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-Advantages: -easy to design and build - use very little materials - can be built quickly -Disadvantages: - might need anchors to the ground - parts have to fit together precisely - might need to be braced or reinforced
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What are advantages and disadvantages to Shell structures?
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Advantages: - completely empty so make great containers - use very little building material Disadvantages: - flat materials do not easily form shells - careful assembly is required -outside forces can easily damage the shell
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What is a load?
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What is a load? The weight carried or supported by a structure
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On your whiteboard, list as many functions of a structure that you can think of… TPS
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On your whiteboard, list as many functions of a structure that you can think of… TPS
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On your whiteboard, list as considerations when choosing a material… TPS
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What are three types of materials?
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What are three types of materials and examples of each? Composite (particle board), Layered (plywood) and Woven and Knit (tissue)
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What are two main types of joints?
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What are two main types of joints? Mobile and Rigid
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What are five types of rigid joints?
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What are five types of rigid joints? Interlocking shapes, fasteners, ties, adhesives, melting
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28. Mass
If you understand how mass causes a load force on a structure, you will find it easier to make strong, efficient designs.

29. Mass
Mass = the amount of matter in an object Unit for mass = grams (g), pounds (lb), ounce (oz) Measured using a scale or balance

30. Practice on whiteboard converting units of mass

31. Mass
1 g = 1000 mg 1 kg = 1000 g 1) 45 kg = g 2) 35 g = mg 3) g = kg 4) mg = g

32. Mass
1 g = 1000 mg 1 kg = 1000 g 1) mg = g 2) g = kg 3) kg = g 4) g = mg

33. Mass
1 g = 1000 mg 1 kg = 1000 g 1) mg = g 2) g = kg 3) kg = g 4) g = mg

34. Mass
1) 9.87 kg = g 2) 47.8 dg = hg 3) cg = mg 4) 689 dag = kg

35. Mass
1) 9.87 kg = 9870 g 2) 47.8 dg = hg 3) cg = 4.56 mg 4) 689 dag = 6.89 kg

36. Not the same thing!!!! But…why?
Mass and Weight
Not the same thing!!!! But…why?

37. Weight
Weight = force of gravity on the mass of an object – measured in Newtons (N)

38. Convert Grams into Newtons
Textbook…use reading strategy…. p F= m x a 1 kg = 10 N

39. Convert the following into newtons
4.5 kg = N 0.36 kg = N kg = N 98 kg = N

40. Convert the following into newtons
4.5 kg = 45 N 0.36 kg = 3.6 N kg = 1367 N 98 kg = 980 N

41. Convert the following into Kilograms
4.5 N = kg 0.36 kg = N *136.7 g = N *98 N = g

42. Convert the following into Kilograms
4.5 N = 0.45 kg 0.36 kg = 3.6 N g = N 98 N = 9800 g

43. Draw a labeled force diagram for….

44. Force
Forces are stresses such as a push or a pull Unit for any force = Newtons (N) Force is measured using force meters or spring scale Force has a direction and an amount.

45. Force diagram p304

46. Weight is one of many types of forces that act on structures.

47. Stable structures p329
Stability – ability to resistance to tip and stay balanced Balancing on ball – sit, superman challenge!videos of people standing on it Centre of gravity – the point at which all of the weight of an object appears to be concentrated and balanced when standing or rotating or moving - the lower the center of gravity, the more stable the structure

48. Balancing Act p
Balancing nails, paper cut out ie. bird, clown, etc. Create symmetry: The quality of being made up of exactly similar parts facing each other or around an axis. - Help to distribute the load, balance the center of gravity

49. Finding COM
Cut out the shape. Pin one shape to a bulletin board (NOT THE WALL!) Hang the string with the weight from the pin and draw the line where the string goes. Turn the shape and pin it again to the bulletin board. Hang the string and draw where the line is. Turn it again and hang the string and draw where the line is. This should give you the center of gravity.

51. Do we need to go through this for a square, triangle?
Finding COM
Do we need to go through this for a square, triangle?

54. External force – stresses that act on a structure from outside it
Types of Forces
External force – stresses that act on a structure from outside it

55. Types of Forces External forces include:
LIVE LOADS – changing or non- permanent force acting on a structure
ie. wind, people, snow, rain, impact forces caused by objects colliding with the structure, friction

56. Types of Forces Dead loads – permanent force acting on a structure
Includes the weight of the structure itself

57. Types of Forces
Internal force – stresses within the materials from which a structure is made - Can change the shape or size of a structure resulting in deformation

58. Tension forces – stretch a material by pulling its ends apart
Internal Forces
Tension forces – stretch a material by pulling its ends apart
- Tensile strength measures the largest tension force the material can stand before breaking

59. 2) Compression forces – crush a material by squeezing it together
Internal Forces
2) Compression forces – crush a material by squeezing it together
- Compressive strength –measures the largest compression force a material can withstand before losing it shape or breaking into pieces

60. Internal Forces
3) Shear 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 stand before ripping apart

61. Internal Forces
4) Torsion forces – twist a material by turning the ends in opposite directions
- Torsion strength – measures the largest torsion force the material can stand and stills spring back to its original shape

63. Playdough time Roll the playdough into a roll.
Slowly twist the playdough. What type of force is this? Repeat step 1.
Slowly pull up and push down on the playdough at the same time. What type of force is this? Repeat step 1
Slowly push the ends of the playdough together. What type of force is this Repeat step 1.
Slowly and gently pull the playdough apart. What type of force is this?

64. Identify that Stress (External/Internal)
Classify the following forces as internal or external:
Red =
Yellow =
Purple =
Green =
Blue =

65. Identify that Stress Red = external (friction)
Yellow = internal (tension)
Purple = external (friction)
Green = internal (weight)
Blue = internal (compression)

66. Identify that Load (Live/Dead)#4
Live Load #2 #1
Live load
Live load #3 #5
Live Load #6

67. Identify that Force #1 #2

68. Identify that Stress

69. Identify that Stress

70. Identify that Stress

71. Identify that Stress

72. Identify that Stress

73. Building Big with forces -see it in real life
Review types of forces
Building Big with forces -see it in real life

74. Resisting Stress
A) Materials that have high tensile strength have strong forces pulling a few other particles together

75. Resisting Stress
B) Materials that have low shear strength, like graphite, have particles arranged in layers, but the forces between the layers are relatively weak

76. Resisting Stress
C) Materials with high torsion strength, like rubbers, have particles that are attracted in all directions to the other particles around it

77. How Structures Fail page 315
Failure – loss of shape, change in size, breakage, deformation, cracking Each type of internal force can cause certain types of damage.

78. How Structures Fail page 315
Shear failure– is due to compression
- one section may slide over another section along the weakness in the material

79. How Structures Fail page 316
2) Bend or Buckle – again due to compression distribute the load unequally causing compression on the inside of the curve and tension on the outside of the curve

80. How Structures Fail page 316
3) Torsion – brittle structures will break while flexible structures can get tangled

81. Where a structure fails, is usually at the joints – how they are put together
Do you remember the types?
Mobile joints
Rigid joints
Fasteners
Interlocking shapes
Ties
Adhesives
Melting

82. Designing with forces
Distribute the load throughout the structure so that no single part is carrying most of the load
Direct the forces along angled components so that the forces hold pieces together instead of pulling them apart.
Shape the parts to withstand the specific type of force they are likely to experience.

83. Designing with forces
Turn to p and take notes on how the three problems are solved Work with group to use a piece of paper to support a pop

84. Firm Foundation p337
Foundation is the base. A firm and strong foundation can be built one of three ways…

85. Firm Foundation p337 Find something solid
- bedrock, undisturbed soil, pilings that sit on the bedrock

86. Firm Foundation p337
2) Make a solid layer - make layers of rock, soil, clay etc to build a base

87. Firm Foundation p337
3) Spread the Load - weight of structure is spread over a large area - footings (a concrete foundation) that are wider than the walls themselves - footings are below the frost line

88. Redo the spaghetti challenge!

89. Engineering ideas (egg drop, cardboard furniture, making a nest, arm and leg, roller coaster
Egg drop demo
Environmental impact, needs and wants (reuse ?
Supply and demand

90. - Quiz before unit exam - Review