# Quantities¶

The following is a list of all physical quantities relevant to SEA.

## General quantities¶

frequency
Frequency f is the number of occurrences of a repeating event per unit time and has the unit hertz (Hz).
angular frequency

Angular frequency is the frequency of an oscillation in unit radians per second (rad/s).

speed of sound

Speed of sound c describes the speed at which a wave passes through a medium.

Phase speed

Group speed

## Mechanical quantities¶

aera moment of inertia
second moment of inertia
Area moment of area, also known as ‘second moment of inertia, ‘moment of inertia of plane area, or ‘second area moment’, is a geometrical property of an area which reflects how its points are distributed with regards to an arbitrary axis. It has unit (m^4).
torsional moment of rigidity
The torsional moment of rigidity J

Radius of gyration or gyradius is the name of several related measures of the size of an object, a surface, or an ensemble of points. It is calculated as the root mean square distance of the objects’ parts from either its center of gravity or a given axis.

## Energy quantities¶

velocity
The velocity v
velocity level

The velocity level is given by

where is a reference velocity.

mobility
The mobility Y describes how easily a body moves when subject to a force.
energy
The energy E
power dissipation

The power dissipation P in a subsystem i is given by

where is the loss factor of the subsystem.

## Material quantities¶

density
The density
young’s modulus
Young’s modulus E, also known as the tensile modulus or elastic modulus, is a measure of the stiffness of an elastic material, and has the unit pascal (Pa).
bending stiffness
flexural rigidity
The bending stiffness or flexural rigidity D.
shear modulus
Shear modulus G or modulus of rigidity, is defined as the ratio of shear stress to the shear strain, and has the unit pascal (Pa).
bulk modulus
Bulk modulus K of a substance measures the substance’s resistance to uniform compression. It is defined as the ratio of the infinitesimal pressure increase to the resulting relative decrease of the volume, and has the unit pascal (Pa).
poisson’s ratio
Poisson’s ratio is the negative ratio of transverse to axial strain. Poisson’s ratio is dimensionless.
loss factor

Loss factor describes the amount of energy lost per cycle.