1. 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!

2. 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

3. 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

4. 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

5. 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)

6. 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

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

8. 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

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

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