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# Materials

Question | Answer |
---|---|

What is Hooke's law | The extension of a spring is directly proportional to its tension, within the limit of proportionality |

What is the formula for Hooke's law | F=kx |

What is the limit of proportionality | The point at which F is no longer proportional to x |

What is the elastic limit | The point beyond which an object no longer returns to its original dimensions once the force is removed |

What is the equation for strain | ε=x/L |

What are the units for strain | Strain has no units because it is a ratio |

Why is the extension per unit force smaller for objects with a larger cross sectional area | The load is being supported over a larger cross sectional area |

What is the equation for stress | σ=F/A |

What is the equation for Young's modulus | E=σ/ε |

Define strain | Extension per unit length |

Define stress | The force per unit area of a material, where force is at right angles to the surface |

Define Young's modulus | The stress to strain ratio within the limit of proportionality (define sub terms: stress and strain) |

Define UTS | Ultimate tensile strength, the maximum stress before failure |

Define Elastic behaviour | Returns to original dimensions when force is removed |

Define Plastic behaviour | Does not return to its original dimensions when the force is removed |

Define stiffness | The force to extension ratio within the limit of proportionality |

Define malleable | Under compression, can be beaten out into a sheet,may lose strength |

Define ductile | Under tension or extension can be drawn out into a wire, does not lose strength |

Define hardness | Resistance to scratching or abrasion |

Define brittle | Fails or breaks before plastic deformation |

Define tough | -Difficult to break -Resistant to deformation -Absorbs energy under compression |

Define strength | Withstands high stresses before failure |

Define viscosity | Resistance to flow |

What is Moh's scale of hardness | 1:Talc 2:Gypsum 3:Calcite 4:Fluorspar 5:Anathasite 6:Orthoclose 7:Quartz 8:Topaz 9:Corundum 10:Diamond |

What type of test do we do to determine a materials position in the Moh's scale of hardness | Scratch test |

Define density | The mass per unit volume |

What is the equation for density | ρ=m/v |

How do we calculate density for a regular solid | -Measure mass using balance -Measure dimensions with vernier calipers -Calculate volume -Calculate density |

How do we calculate density for a liquid | -Measure mass of empty measuring cylinder -Pour liquid in -Measure volume of liquid -Measure the mass of the cylinder when full -Subtract the mass of empty cylinder -Calculate density |

How do we calculate the density of an irregular solid | -Measure mass -Immerse object on a thread into a eureka can -Measure the volume of water displaced -Calculate density |

What does the area under a Fx graph represent | Elastic potential energy stored in object OR the work done in stretching object |

What is the equation for elastic potential energy | Ee=0.5kx^2 |

How do we find the area under a curve | -Choose square measurement -Calculate joules per square -Count squares and add triangles -Multiply no of squares by joules per square REMEMBER to mark up the graph |

Why is there a difference between the Fx graphs for loading and unloading | Some of the energy stored in the object is transferred to the internal energy of the molecules, due to friction |

Explain the stretching process for rubber | -Rubber is a polymer -When unstretched the molecules are tangled -When stretched they straighten out -When tension is removed it returns to its original length |

Explain the stretching process for Polythene | -When unstretched molecules are tangled -When stretched they straighten out -When tension is removed it does not return to its original shape |

Define polymer | A chain of repeating monomers |

Define creep | A material moving by dislocation |

Define netting | A decrease in x-sectional area |

Define yield point | A large extension is produced for a very small increase in force |

Define laminar flow | Each particle has a constant velocity, it tends to occur at low velocities. |

What is the criteria for fluid diagrams | -At least 5 paths -Paths can't cross -Recumbent flow must be >180 degrees |

Define turbulent flow | Velocity is not constant for each particle, back eddies form, tends to occur at high velocities |

What is the equation for stokes law | F=6πrηv |

What is the equation for terminal velocity | v(term)=(2r^2 g(ρ(s)-ρ(l)))/9η |

For a liquid what is the relationship between temperature and viscosity | Temperature increases, viscosity decreases |

For a gas what is the relationship between temperature and viscosity | Temperature increases, viscosity increases |