Science- Technology Ch. 12/13
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82 terms
Terms | Definitions |
|---|---|
 Define: Technical Object | any item humans use to make a task easier. Made of one or more materials. |
| Define: Constraints | different types of stress a material undergoes. There are 5 main types of constraints. |
| What are the different constraints? | Compression (Crushing) - stapler Tension (Stretching) - pulling plastic Torsion (Twisting) - body Deflection (Bending) - rope Shearing (Cutting) - paper |
| What are the types of deformation? | Elastic, Plastic and Fracture |
| Elastic: | a temporary change in shape or dimension of the material, when constraint is removed the material returns to its original form |
| Plastic: | permanent change in shape and/or dimension, when constraint is removed the material remains deformed |
| Fracture: | constraint is so intense that the material breaks |
| Define: Mechanical Properties | describes how it reacts when subjected to one of more constraints |
| What are the 6 mechanical properties? (hating everyone rlly doesn't make sense) | hardness, elasticity, resilience, ductility, malleability, stiffness |
| Hardness: | ability to resist indentation or abrasion |
| Elasticity: | ability to return to original shape after constraint |
| Resilience: | ability to resist shocks without breaking |
| Ductility: | ability to be stretched without breaking |
| Malleability: | ability to be flattened or bent without breaking |
| Stiffness: | ability to retain their shapes when subjected to constraints |
| Other properties? | Resistance to corrosion: ability to resist the effect of corrosive substances Electrical conductivity: ability to carry an electrical current Thermal conductivity: ability to transmit heat |
| Degredation of a material: | the decline in some of its properties due to the effects of the surrounding environment. All materials eventually degrade, but at different rates |
| Protection of a material: | the application of procedures that prevent or delay degradation |
| What are the 5 categories of materials? | 1. Wood and Modified Wood 2. Ceramics 3. Metals and Alloys 4. Plastics 5. Composites |
| Wood: | material obtained by harvesting/processing trees hardwood = deciduous trees softwood = conifers |
| Properties: | hard, elastic, tough, easily shaped, light |
| What is modified wood? | treated wood or material made from wood mixed with other substances (ex. glue, preservatives) |
| Cons of wood: | It can degrade easily and quickly due to its organic origin |
| Protective mechanism: | varnish, paint, other protective coatings, treated wood: dipped in alkaline solutions with Cu (green color) or heating wood to high temp |
| Ceramic: | a solid material obtained by heating inorganic matter containing various compounds, usually oxides (when heated, H20 evaporates, rearranging and strengthening the bonds) Ex: clay makes pottery, sand makes glass |
| Properties: | low electrical conductivity (good for insulating electronics), corrosion resistant, fragile but resislient, durable |
| Metals and Alloys: | a metal is a material extracted from a mineral ore. Metals are shiny and good conductors of electricity and heat. They are ductile and malleable |
| Define: Alloy | mixture of a metal with one or more other substances (metallic or nonmetallic) Ferrous Alloy: main part is Fe |
| Main cause of degredation? | Oxidation |
| What is the steel heating treatment and why is it done? | Heating steel to enhance mechanical properties |
| Plastics: | materials made of polymers, additional substances can be added to change the properties, poor conductors of electricity and heat. Developped from petroleum and natural gas monomers and arranged in chains to form polymers |
| Thermoplastics: | become soft when heated to be molded, retain their shape when cooled |
| Thermosetting plastics: | remain permanently hard, even when heated (kayaks) |
| What are the causes and preventions of degradation? | Penetration of a liquid prevented by waterproofing coating. Oxidation prevented by adding antioxidants (ex. carbon black). UV rays prevented by adding pigment that absorbs UV rays. |
| Composites: | combining materials from different categories to obtain a material with enhanced properties made of 2 parts: a matrix and reinforcements |
| What do the two parts do? | A matrix provides support while the reinforcements are inserted into the matrix to strengthen it |
| What are the three matrices? | Plastic matrices- thermosetting plastics are preferred, also called resins (durability, light, resilient, low cost) Metallic matrices- made from metals or alloys (ductility, thermal/electrical conductivity, stiffness) Ceramic matrices- made from ceramics, often glass (durability, heat resistance) |
| What are the three reinforcements? | Fiberglass- made of glass (ceramic) in the form of fibres (length, diameter and type of glass varies) (props:stiff, corrosion resistant) Aramid Fibres- known as "Kelvar" one of few plastics used as reinforcements (props: low density, resilient) Carbon Fibres- made by carbonizing polymers, mostly polyacrylonitriles (props: stiff, low density, electrical conductivity) |
| Define: Drafting | the process of creating technical drawings to determine the dimensions of technical objects prior to their construction |
| Define: Projections | the representation of a 3D object on a 2D surface |
| What are the two types? | Isometric projections and multiview projections |
| Define: General Arrangement | a technical drawing representing the overall appearance of an object, usually drawn to scale. |
| Define:Title Block | bottom of the page including name, date, title and scale |
| Define: Exploded View | the various parts of the object are separated from one another (isometric projection) |
| Define: Detail Drawings | A drawing specifying all the relevant info for manufacturing parts |
| Define: Dimensional Tolerance | indicator of the max acceptable difference between a specified measurement and the actual measurement of the finished product |
| Define: Functional Dimensioning | specifies the information required for the object to work |
| Define: Developments | the representation of the surface area required to make a part by bending it |
| When do you being manufacturing? | Once you have picked your materials and drawn the shapes and dimension of your technical object |
| Define: Manufacturing | a series of operations resulting in the creation of a technical object |
| Define: Tool | instrument used in the manufacturing of an object |
| Difference between hand tool and machine tool? | Hand tool the force comes from the person using them and machine tools are help and operated by other forces than human |
| What are the 3 stages of the manufacturing process? | 1) measuring and laying out parts (measuring angles, lengths, diameters and marking it down on material) 2) machining (machining is shaping the material, roughing is cutting the approx. shape of finished part) 3) assembling and finishing (putting the pieces together and protecting the material by polishing, varnishing, dying) |
| What are machining techniques? | cutting: giving a material a desired shape drilling: making a hole in a material tapping: screw threads are formed inside holes drilled into a material (indentation) threading: screw threads are formed around a rod (bulges out-like a screw) |
| Define: Mechanical Engineering | focus on design, production, analysis, working and improvement of technical objects with moving parts |
| How many different pieces and what are they? | There must be 2 different pieces Components- (2 or more) part or fluid that moves Linking- part that connects the moving components |
| What are the different categories of links? | Direct or Indirect Rigid or Flexible Removable or Non-removable Complete or Partial |
| How many ways can an object move and what are they? | 6 ways: 3 directional ways: left and right on the x axis, up and down on the y axis, front and back on the z axis 3 rotational ways: round the x, round the y, round the z |
| What do the degrees of freedom define? | The degrees of freedom define which way the mechanical movement exists |
| Define: guiding control | when an object moves in a mechanical way, it can be "guided" or "controlled" to move in a certain way. The guide is the component that does the controlling and directs the movement |
| What are the 3 types of guiding? | Translational- movement in one straight direction Rotational- movement around a given component Helical- combination or a translation and rotation |
| Define: Adhesion | idea that two objects can remain in contact and not slip. The resulting force is called friction. |
| Easiet and most effective way to reduce adhesion? | Use a lubricant!! |
| What are the 5 factors adhesion depends on? | 1) What materials it is made out of (rubber on rubber= adhesions but silicon on metal= less adhesion) 2) temperature (warmer=more adhesion) 3) Smoothness/Roughness (rough= more adhesion) 4) Force applied (heavy object= more adhesion) 5) What is between them (lubricant= less adhesion) |
| What are the three types of lubricants: | liquids (oil, glue, water) semisolid (vaseline, glue stick) solid (wax) |
| Define: Transmission of motion | is when motion is transmitted from 1 moving object to another. Ex: on a bike, your feet more the pedals, which move the gears, which move the chain which moves the wheels. This is a motion transmission system. |
| What are the parts it is broken up into? | Driver- component receiving the initial movement Intermediate- component transfering motion from driver to driven (not always needed) Driven- component that executes the motion of the driver |
| What are the 5 types of Motion Transmission Systems? | 1) Gear Trains 2) Chain and Sprocket 3) Worm and Worm Gear 4) Friction Gear System 5) Belt and Pulley |
| 1. Gear Train | used in close contact where the teeth transmit the motion. It is reversible. 3 things to consider: the teeth must be same size and shape to work properly, gear type (parallel or perpendicular), gear size (big= slow, small= fast) |
| 2. Chain and Sprocket | gears are not directly in contact (sprocket), chain connects the two distance parts. It is reversible. |
| 3. Worm and Worm Gear | a screw shaped gear known as a worm screw/shaft that touches another gear. This is not reversible. 2 constraints: teeth and grooves of worm need to be the same size, the worm is always the driver component |
| 4. Friction Gear System | Uses friction instead of teeth to move. It is reversible. 3 types exist: straight (parallel), bevel (perpendicular) and spherical (rotational to each other). Larger gear= slower the rotation. Higher adhesion= more friction= more contact for movement |
| 5. Belt and Pulley | It is reversible. |
| Which is the slowest system? | Worm and Worm Gear because everytime the worm turns 1 full time, the worm gear only moves by 1 tooth. Therefore the more teeth there are the more the speed will reduce. |
| Speed change in a gear train | Gear train/belt and pulley speed is directly related to the diameter. Increase speed, driver must be bigger than driven. To decrease speed, driver must be smaller than the driven component. Maintain speed, same size. |
| Define: Motion Transformation System | rotation to a translation or vice versa |
| What are the motion transformation systems? | Rack and Pinion Screw Gear System Type 1 Screw Gear System Type 2 Cam and Follower Slider-crank mechanism |
| 1. Rack and Pinion | rack is the straight piece with teeth pinion is the round piece with teeth like a bumper car. Rotation to translation or vice versa. |
| 2. Screw Gear System Type 1 | YOU turn the screw and the nut moves back and forth. Rotation to translation. Not reversible. (Car jack) |
| 3. Screw Gear System Type 2 | YOU turn the nut and and screw moves back and forth. Rotation to translation. Not reversible (corkscrew). |
| 4. Cam and Follower | cam is the round part that may or may not have a funny shape follower is the straight piece moved by the cam. Rotation to translation. Not reversible. (Sewing machine) |
| 5. Slider-Crank Mechanism | slider= part (box) that moves up and down crank= piece attached to the slider and a gear that moves rotationally Reversible!!! (motor- trans to rot) |
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