Chapter 12 - Properties of Materials (Up to top of pg 208) Flashcards
What is the equation for density?
Density = Mass / Volume
What is aerogel and what is it used for?
A very low density insulator that is often used in airplane or space missions. It is 99.8% air
What are compressive forces?
Forces that tend to squeeze an object and reduce its size in the direction in which it was applied
What are tensile forces?
Forces that act to pull or stretch an object e.g. the wires/ropes that hold up a lift
What is a spring constant and what does it mean if the spring constant is large?
The spring constant is a measure of how hard it is to bend or stretch a spring. The larger it is, the harder it is to stretch the spring - it is stiff
What is the equation form of Hooke’s Law?
Force (N) = Spring Constant (N/m) x Change in length or extension (m)
What is the elastic limit?
The load above which a material becomes plastic and is permanently deformed
What does it mean if a material is brittle?
It shows little to no plastic deformation before it breaks
What is the feature of ductility?
The ability for a material to be drawn into wires - if it can successfully be so, then it is ductile
How does a ductile wire break in comparison to a brittle wire?
The ductile wire would ‘neck’ - get thinner and taper - before fully breaking, whereas the brittle wire would shear flat and unevenly when it breaks
What is elastic strain energy?
Energy that is stored in a material from stretching it. It is equal to the amount of work done to the material from the aforementioned stretching, which depends on the average force supplied and the extension of the material
What are two equations for elastic strain energy?
Elastic strain energy = 1/2 x Force x Extension = 1/2 x Spring Constant x Extension^2
On a graph measuring extension against force, what does the area under the graph represent?
The work done to the material in order to stretch it. This can be figured out in sections - where it obeys Hooke’s Law and where it breaches its limit of proportionality. This can be found from differentiation as well as simple area finding when the relationships are linear
What would the energy-extension graph look like for a rubber band being stretched? (in words)
It would start off with a medium extension for a medium amount of force, then go to a large extension for a small amount of force, and then get harder again to a medium extension for a large amount of force
How much do two strings joined in series stretch in comparison to one of the same type that is stretched normally?
They would extend double as much
