Chapter 11 - Materials Flashcards
What is the equation for density?
p = m/v
What is Hooke’s Law?
The force needed to stretch a spring is directly proportional to the extension or compression of the spring from its natural length.
F = kΔL
where k = spring/stiffness constant
where F = tensile or compressive force
What is the elastic limit?
The maximum force that can be applied to a spring such that the spring returns to its natural length when the force is removed.
The point beyond which a material is permanently stretched and suffers plastic deformation.
Describe the nature of a rubber band when stretched.
A rubber band at first extends easily when it is stretched and then it becomes increasingly difficult to stretch further.
Describe the nature of a polythene strip when stretched.
A polythene strip ‘gives’ and stretches easily after its initial stiffness is overcome and then becomes more difficult to stretch.
What is the equation for tensile stress?
What is its unit?
σ = T/A
Unit: Pa or Nm-2
What is the equation for tensile strain?
What is its unit?
ε = ΔL/L
Unit: None as it is a ratio.
What is the limit of proportionality?
The point beyond which Hooke’s Law is no longer obeyed by the material.
It is not always the same point as the elastic limit.
What is the Young Modulus, E?
E = σ/ε
It is constant for a material below its limit of proportionality.
What is a brittle material?
A material which snaps without any noticeable yield (i.e. it does not undergo plastic deformation).
What is a ductile material?
A material which can be drawn into a wire.
What is elasticity?
A property of a solid material that returns to its original shape after it has been deformed, once the forces that deformed it have been removed.
What is the equation for pressure?
P = F ÷ A
How can you find the volume of an irregular solid?
Submerge it into water and measure the apparent change in volume of the water.
What is the spring constant a measure of?
The stiffness of a spring.
