young’s modulus 10:00 Particle Physics :30 3 Experiments 12:00

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Presentation transcript:

young’s modulus 10:00 Particle Physics 101 10:30 3 Experiments 12:00 Lunch Break! 13:00 Young’s Modulus of Sweets 13:30 15:00 Hometime!

what will we cover today? how does the structure of my snowboard effect performance? Behaviour of materials Tension and compression Stress, strain and Young’s Modulus Elastic and plastic deformation Testing materials… and sweets

tension + compression TORSION COMPRESSION SHEAR BENDING TENSION Returns to original shape = elastic BENDING TENSION Deformation = due to force in one dimension Object + Stretch / Shear / Compression = change shape Remains deformed = plastic / inelastic

elastic materials Extension proportional to load = Hooke’s Law Hooke’s Law: F = kx k = spring constant = gradient of F vs. x Force Extension (m) Fracture!! Plastic You have probably done an experiment like the one shown here – using a load to stretch a spring, and the increase in length (extension) of the spring is proportional to the load. If a spring (or anything else) behaves like this, with extension proportional to load, we say that it obeys Hooke's law (the gradient of the straight section of a force-extension graph). At first, if you remove the load, the spring returns to its original length. This is elastic behaviour. Eventually, the load is so great that the spring becomes permanently deformed. You have passed the elastic limit. He also made the first microscope and came up with the word ‘cell’ Elastic

just hang on in there… STIFF SPRING SOFT SPRING What if my spring constant changes? STIFF SPRING SOFT SPRING Important in seat belt design Have to replace after a crash (go passed elastic limit)

stress + strain Stress is the pressure a material is under= force per unit area. σ = F/A Strain is a measurement of how much a material has stretched/ deformed. Ratio between the original length of the material and the amount it has extended by ε = x/L What are the units of stress? [F] = N, [A] = m2 What are the units of strain? [x] = m, [L] = m Young’s modulus is a measurement of the stiffness of a material, it tells us how much a material will extend (strain) under a given pressure = stress / strain E = σ/ε

stress-strain for a ductile material What’s the gradient equal to? E = σ/ε

stress-strain Stress Strain Brittle material- strong with little strain at high stress. Fracture of a brittle material is sudden, with no plastic region Strong material, not ductile- stretches very little, then breaks! Stress Strain Ductile: After elastic region = ‘necking’ then permanent deformation in plastic region Plastic: very small elastic region

testing materials bubbles represent a material and how much a range of density/young's modulus

what are we measuring? Breaking Stress Young’s Modulus Force Extension