Materials

What is polythene?
Polythene is made of long chained molecules which extend elastically and rotate around bonds - flexible.
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How are polymers made less flexible and more strong?
Polystyrene has benzene rings to resist rotation and bakelite is cross-linked.
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How can rubber be treated?
Rubber is vulcanised with sulfur to make it stronger.
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Is polythene crystalline or amorphous?
Polythene is semi crystalline. When stretched, it necks and the area of crystallinity increases.
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How does ceramic bonding affect strength and flexibility?
Ceramics can be covalent or ionic with directional bonds. The atoms are in a strong structure but are stiff and brittle.
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What are polycrystalline materials? What does slow cooling achieve?
Polycrystalline materials have amorphous grain structures with crystalline grains which meet at grain boundaries. Slow cooling produces single crystals.
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How do cracks spread in ceramics? Why don't they in metals?
Cracks propagate in ceramics as stress is deflected to the crack causing the material to unzip. In metals, the stress is spread and the material plastically deforms to make the crack broader.
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How do dislocations improve metals?
Metals are crystalline. They can have dislocations which make metals malleable and ductile as atoms move one at a time requiring less force.
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Why are metal alloys stronger?
Metal alloys have other elements which pin down dislocations.
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For gold atoms, how can you find length?
To calculate the volume of one gold atom, calculate the number of atoms in 1m^3 and divide 1m^3 by this to find volume of each atom. To find length, get cube root
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When metals extend, what happens to bonds?
When metals extend elastically, bonds are stretched but will return to normal.
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Young Modulus measures stiffness of a.... . What is the formula?
Young Modulus is stiffness for a specimen. E= stress/strain
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What do stress and strain compare?
Stress compares specimens while strain compares materials.
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What is Hooke's Law?
F=kx up to a limit of proportionality. K is the stiffness which relies on the specimen.
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What happens beyond the elastic limit?
Beyond the limit of proportionality plastic deformation occurs.
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What's the formula for energy?
E = 1/2Fx
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What formula is derived from Rayleigh's Oil Drop experiment?
4/3 * π * r^3 = πR^2h
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For springs in parallel, why is total k doubled?
Force in each spring is halved.
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What device can measure force?
A Newton-metre can measure force exerted on a spring
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Other cards in this set

Card 2

Front

How are polymers made less flexible and more strong?

Back

Polystyrene has benzene rings to resist rotation and bakelite is cross-linked.

Card 3

Front

How can rubber be treated?

Back

Preview of the front of card 3

Card 4

Front

Is polythene crystalline or amorphous?

Back

Preview of the front of card 4

Card 5

Front

How does ceramic bonding affect strength and flexibility?

Back

Preview of the front of card 5
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