Materials Flashcards
State Hooke’s law
The extension or compression of an object is directly proportional to the force on that object, provided the limit of proportionality (elastic limit) has not been exceeded
What is the equation to work out force constant or spring constant (k)?
k = F/x
For a stiffer spring, k is higher
How do you work out spring constant for springs in series?
Ktotal = K1 + K2 + K3 ……
How do you work out spring constant for springs in parallel?
1/Ktotal = 1/K1 + 1/K2 + 1/K3 …..
State the equation, symbol and unit for stress
Stress = F/A, where F is force and A is the cross sectional area
Symbol - σ
Unit - Nm^-2 (Pa)
State the equation, symbol and unit for strain
Strain = x/L, where x is extension and L is the original length of the spring
Symbol - ε
No units
What is the equation for Young Modulus?
E = σ/ε
Young Modulus = stress/strain
This can also be written as E = F/A / x/L
And rearranged to make E = FL / Ax
What do you call a pair of forces that compress an object?
Compressive forces
What do you call a pair of forces that extend an object?
Tensile forces
What is the area under a force/extension graph equal to?
Work done
Define limit of proportionality
It is the point at which the deformation of a spring ceases to be linear. It also becomes permanent - the spring will not return to its original length when the force is removed
State and define the two phases of a stress/strain graph
Elastic phase - obeys Hooke’s law
Plastic phase - doesn’t obey Hooke’s law
What resolution does a vernier scale have?
1x10^-6m
State the properties of a stress/strain graph for a brittle material
- straight diagonal line through origin
- obey Hooke’s law
- elastic behaviour only
- breaks at B - the breaking point
State the properties of a stress/strain graph for a ductile material
- elastic and then plastic behaviour
- obey Hooke’s law up until P (limit of proportionality)
