11 Materials Flashcards
what is density?
mass per unit volume
how do you measure the density of a regular solid?
- mass - top pan balance
- measure dimensions using vernier calipers/micrometer + calculate volume
how do you work out the density of a liquid?
- mass - measure mass of an empty measuring cylinder. pour some of the liquid into the cylinder measure mass again with the cylinder + liquid. mass = total - cylinder
- volume - measure volume directly from cylinder
how do you measure the density of an irregular solid?
- mass - balance
- immerse object on a thread in liquid in measuring cylinder. observe increase in liquid level. this is volume
what is an alloy?
a mixture of two metals
how do you calculate the density of an alloy?
𝜌 = (𝜌₁V₁ + 𝜌₂V₂) / V
what is Hooke’s law?
the force needed to stretch a spring is directly proportional to the extension of the string from its natural length
what is the formula for Hooke’s law?
F = kΔL
What is a spring’s elastic limit?
point beyond which a wire is permanently stretched
What is the same for springs which are stretched in parallel?
The extension is the same for each spring
What is the same for springs which are stretched in series?
The tension in each spring is the same which is equal to the weight W
From a force/extension graph, how is the energy stored in a stretched spring calculated?
Area under the graph
E = 1/2 ⨉ F ⨉ ΔL = 1/2 ⨉ k ⨉ ΔL²
What is elasticity?
Of a solid material
ability to regain its shape after it has been deformed/distorted and the forces that deformed it have been released
what is the deformation that stretches called?
tensile
what are deformations that compresses called?
compressive
what is tensile stress?
force per unit area of cross section in a solid perpendicular to the cross section
what is tensile strain?
extension per unit length of a solid when deformed
What is the Young modulus?
the constant value of stress/strain for a material
what is the yield point of a material?
the point at which the stress in a wire suddenly drops when the wire is subjected to increasing strain
what is plastic deformation?
the deformation of a solid beyond its elastic limit
What is ultimate tensile stress?
tensile stress needed to break a solid material
also known as breaking stress
what is the stiffness of a material related to on a stress strain graph?
the gradient of the stress strain line which is equal to the Young modulus
what is the strength of a material?
the ultimate tensile stress of the material
what does brittle mean?
snaps without stretching or bending when subject to stress
what does ductile mean?
stretches easily without breaking
what do the loading and unloading curves of a metal wire look like?
they are the same provided its elastic limit is not exceeded ∴ returns to its original length.
if the elastic limit is exceeded, the unloading line is parallel to the loading line
what do the loading and unloading curves of a rubber band look like?
- returns to the same unstretched length
- unloading curve is below the loading curve except at zero and maximum extensions
what do the loading and unloading curves of a polythene strip look like?
- the extension during unloading is greater than during loading.
- the strip does not return to the same initial length
- suffers plastic deformation
what is strain energy?
the work done to deform an object
what is the formula for the elastic energy stored in a stretched wire and where is it derived from?
1/2 T ΔL
from the area under a force extension graph
