### Key Terms

- breaking stress (ultimate stress)
- value of stress at the fracture point

- bulk modulus
- elastic modulus for the bulk stress

- bulk strain
- (or
**volume strain**) strain under the bulk stress, given as fractional change in volume

- bulk stress
- (or
**volume stress**) stress caused by compressive forces, in all directions

- center of gravity
- point where the weight vector is attached

- compressibility
- reciprocal of the bulk modulus

- compressive strain
- strain that occurs when forces are contracting an object, causing its shortening

- compressive stress
- stress caused by compressive forces, only in one direction

- elastic
- object that comes back to its original size and shape when the load is no longer present

- elastic limit
- stress value beyond which material no longer behaves elastically and becomes permanently deformed

- elastic modulus
- proportionality constant in linear relation between stress and strain, in SI pascals

- equilibrium
- body is in equilibrium when its linear and angular accelerations are both zero relative to an inertial frame of reference

- first equilibrium condition
- expresses translational equilibrium; all external forces acting on the body balance out and their vector sum is zero

- gravitational torque
- torque on the body caused by its weight; it occurs when the center of gravity of the body is not located on the axis of rotation

- linearity limit (proportionality limit)
- largest stress value beyond which stress is no longer proportional to strain

- normal pressure
- pressure of one atmosphere, serves as a reference level for pressure

- pascal (Pa)
- SI unit of stress, SI unit of pressure

- plastic behavior
- material deforms irreversibly, does not go back to its original shape and size when load is removed and stress vanishes

- pressure
- force pressing in normal direction on a surface per the surface area, the bulk stress in fluids

- second equilibrium condition
- expresses rotational equilibrium; all torques due to external forces acting on the body balance out and their vector sum is zero

- shear modulus
- elastic modulus for shear stress

- shear strain
- strain caused by shear stress

- shear stress
- stress caused by shearing forces

- static equilibrium
- body is in static equilibrium when it is at rest in our selected inertial frame of reference

- strain
- dimensionless quantity that gives the amount of deformation of an object or medium under stress

- stress
- quantity that contains information about the magnitude of force causing deformation, defined as force per unit area

- stress-strain diagram
- graph showing the relationship between stress and strain, characteristic of a material

- tensile strain
- strain under tensile stress, given as fractional change in length, which occurs when forces are stretching an object, causing its elongation

- tensile stress
- stress caused by tensile forces, only in one direction, which occurs when forces are stretching an object, causing its elongation

- Young’s modulus
- elastic modulus for tensile or compressive stress