Chapter 11 - Equilibrium And Elasticity Flashcards
First condition for equilibrium:
The sum of all forces on the body is equal to zero.
Second condition for equilibrium:
The sum of all torques about any given point is equal to zero.
Static Equilibrium
If a body is at rest and has no translational or rotational motion.
A body in equilibrium can be..
In uniform translational or rotational motion.
Centre of gravity is..
Treating a body’s weight as though it all acts at a single point.
If we ignore the variation of gravity with altitude, the centre or gravity is the same as:
The centre of mass.
To stop something from tipping over (EG a car), the centre of gravity must be:
Somewhere in the area bounded by supports.
What is stress?
Force per unit area.
What is strain?
The fractional deformation due to stress.
What is Hooke’s Law?
Stress/strain = elastic modulus
What is tensile and compressive stress?
Tensile or compressive force per unit area.
What is tensile strain?
Fractional change in length.
What is the elastic modulus for tension (tensile) called?
Young’s modulus
A large value for Young’s Modulus shows that?
The material is difficult to stretch.
What is the formula for elongation?
Elongation = strain*L0 = deltaL
What is pressure in a fluid?
Force per unit area.
What is bulk stress?
Pressure change.
What is bulk strain?
Fractional volume change.
What is the elastic modulus called for bulk stress and strain?
Bulk modulus.
What is compressibility?
K=1/B
What is shear stress?
Force per unit area for a force applied tangent to a surface.
What is shear strain?
The displacement x of one side divided by the transverse dimension h.
What is the shear modulus?
S = shear stress/shear strain
What is the proportional limit?
The maximum stress for which stress and strain are proportional.
Beyond the proportional limit..
Hooke’s Law is not valid.
What is the elastic limit?
The stress beyond which irreversible deformation occurs.
What is the breaking strength/ultimate strength?
The stress at which the material breaks.
