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Published byShon Jacobs Modified over 9 years ago
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The Wonderful World of… TECHNOLOGY
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MATERIALS External forces produce various effects inside a material. EXAMPLE: *Consider what would happen if an elephant walked in the room and stepped on your pencil. What would the effect be? EXTERNAL FORCE = Elephant weight EFFECT = pencil being crushed
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Different materials react differently to different external forces.
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MECHANICAL CONSTRAINTS “A mechanical constraint describes the stress produced within a material when it is subjected to external forces.” 5 types of constraints: Compression, Tension, Torsion, Bending, Shearing
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COMPRESSION: Force that crushes materials
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TENSION: Force that stretches materials
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TORSION: Force that twists materials
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BENDING: Force that bends materials
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SHEARING: Force that cuts or tears materials
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EXAMPLES: SHOES: CLICKER: WATER BOTTLE:
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What happens when there is TOO MUCH STRESS (constraint) on material? Elastic deformation – Temporary deformation of material. Resumes shape. Plastic deformation – Remains deformed. Fracture – Material ruptures.
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Your Pencils Have you ever asked yourself why pencils are never made out of rubber? Or out of glass?
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MECHANICAL PROPERTIES Determines how a material will react when it is subjected to one (or more) mechanical constraints. Examples of properties: Hardness, elasticity, ductility, malleability, tensile strength
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Resists penetration Reacts to pressure force by elastic deformation
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Regains initial shape Reacts to force by elastic deformation
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Resists physical impacts Reacts to temporary force by elastic deformation.
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http://www.youtube.com/watch?v =j87UWgvetRg Building Design Pulls Structure Upright after Earthquake
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Stretches without breaking Reacts to tension force by plastic deformation.
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Flattens or bends without breaking Reacts to bending or compression force by plastic deformation.
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Resists tension without becoming permanently deformed Reacts to tension force by elastic deformation
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HARDNESSResists penetration ELASTICITYRegains initial shape RESILIENCEResists physical impacts DUCTILITYStretches w/o breaking MALLEABILITYFlattens/bends without breaking TENSILE STRENGTH Resists tension without permanently deforming
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WOOD: p.374 METALS: p.379 ALLOYS: p.380 PLASTICS: p.382
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