Objects are **not rigid**, which are **deformed** by **tension, compression, pressure, or shear**.

conditions for **equilibrium**:

vector sum of all external **forces** and **torques** must be zero.

Relationship between force F, torque τ (or moment M), linear momentum p, and angular momentum L:

$vec tau (vec M)= vec r times vec F$

$vec L = vec r times vec p$

— -

Tensile(Compressive) stress = $frac{F}{A}$

Tensile(Compressive) strain = $frac{Delta l}{l_0}$

Young’s modulus: E = Tensile stress / Tensile strain

— -

Shear stress = $frac{F_{||}}{A}$

Shear strain = $frac x h$

Shear modulus: G = Shear stress / Shear strain

— -

Bulk stress = $ Delta p$

Bulk strain = $ frac{Delta V}{V_0}$

Bulk modulus: K = $-frac{Delta p}{Delta V/V_0}$

Compressibility: 1/K