Physics Formulae/Classical Mechanics Formulae

Lead Article: Tables of Physics Formulae

This article is a summary of the laws, principles, defining quantities, and useful formulae in the analysis of Classical Mechanics.

Mass and Inertia

Mass can be considered to be inertial or gravitational.

Inertial mass is the mass associated with the inertia of a body. By Newton's 3rd Law of Motion, the acceleration of a body is proportional to the force applied to it. Force divided by acceleration is the inertial mass.

Gravitational mass is that mass associated with gravitational attraction. By Newton's Law of Gravity, the gravitational force exerted by or on a body is proportional to its gravitational mass.

By Einstein's Principle of Equivalence, inertial and gravitational mass are always equal.

$M_{\mathrm {inertial} }\mathbf {a} =M_{\mathrm {gravity} }\mathbf {g} \,\!$

Often, masses occur in discrete or continuous distributions. "Discrete mass" and "continuum mass" are not different concepts, but the physical situation may demand the calculation either as summation (discrete) or integration (continuous). Centre of mass is not to be confused with centre of gravity (see Gravitation section).

Note the convenient generalisation of mass density through an n-space, since mass density is simply the amount of mass per unit length, area or volume; there is only a change in dimension number between them.

Quantity (Common Name/s)	(Common) Symbol/s	Defining Equation	SI Units	Dimension
Mass density of dimension n ($V_{n}\,\!$ = n-space) n = 1 for linear mass density, n = 2 for surface mass density, n = 3 for volume mass density, etc	linear mass density $\lambda \,\!$, surface mass density $\sigma \,\!$, volume mass density $\rho \,\!$, no general symbol for any dimension	n-space mass density: $\rho _{n}={\frac {\partial ^{n}m}{\partial x_{n}\cdots \partial x_{2}\partial x_{1}}}={\frac {\partial m}{\partial V_{n}}}\,\!$ special cases are: $\lambda ={\frac {\partial m}{\partial x}}\,\!$ $\sigma ={\frac {\partial ^{2}m}{\partial x_{2}\partial x_{1}}}={\frac {\partial ^{2}m}{\partial S}}\,\!$ $\rho ={\frac {\partial ^{3}m}{\partial x_{3}\partial x_{2}\partial x_{1}}}={\frac {\partial m}{\partial V}}\,\!$	kg m-n	[M][L]-n
Total descrete mass	$M\,\!$	$M=\sum _{i}m_{i}\,\!$	kg m	[M][L]
Total continuum mass	$M\,\!$	n-space mass density $M=\int \rho _{n}\mathrm {d} ^{n}x=\int \cdots \int \int \rho _{n}\mathrm {d} x_{1}\mathrm {d} x_{2}\cdots \mathrm {d} x_{n}\,\!$ special cases are: $M=\int \lambda \mathrm {d} x\,\!$ $M=\int \sigma \mathrm {d} A=\iint \sigma \mathrm {d} x_{1}\mathrm {d} x_{2}\,\!$ $M=\int \rho \mathrm {d} V=\iiint \rho \mathrm {d} x_{1}\mathrm {d} x_{2}\mathrm {d} x_{3}\,\!$	kg	[M]
Moment of Mass	(No common symbol)	$\mathbf {m} =\mathbf {r} m\,\!$	kg m	[M][L]
Centre of Mass	$\mathbf {r} _{\mathrm {com} }\,\!$ (Symbols can vary enourmously)	ith moment of mass $\mathbf {m} _{i}=\mathbf {r} _{i}m_{i}\,\!$ Centre of mass for a descrete masses $\mathbf {r} _{\mathrm {com} }={\frac {1}{M}}\sum _{i}\mathbf {r} _{i}m_{i}={\frac {1}{M}}\sum _{i}\,\!$ Centre of a mass for a continuum of mass $\mathbf {r} _{\mathrm {com} }={\frac {1}{M}}\int \mathbf {r} \mathrm {d} \mathbf {m} ={\frac {1}{M}}\int \mathbf {r} \mathrm {d} ^{n}m={\frac {1}{M}}\int \mathbf {r} \rho _{n}\mathrm {d} ^{n}x\,\!$	m	[L]
Moment of Inertia (M.O.I.)	$I\,\!$	M.O.I. for Descrete Masses $I=\sum _{i}\left|\mathbf {r} \right|^{2}m\,\!$ M.O.I. for a Continuum of Mass $I=\int \left|\mathbf {r} \right|^{2}\mathrm {d} m=\int \left|\mathbf {r} \right|^{2}\rho _{n}\mathrm {d} ^{n}x\,\!$	kg m2 s-1	[M][L]2
Mass Tensor		Components $m_{\mathrm {ij} }\,\!$ Contraction of the tensor with itself yeilds the more familiar scalar	kg	[M]
M.O.I. Tensor	$\mathbf {\mathrm {I} } \,\!$	Components $I_{\mathrm {ij} }\,\!$ 2nd-Order Tensor Matrix form $\mathbf {\mathrm {I} } ={\begin{pmatrix}I_{11}&I_{12}&I_{13}\\I_{21}&I_{22}&I_{23}\\I_{31}&I_{32}&I_{33}\end{pmatrix}}\,\!$ Contraction of the tensor with itself yeilds the more familiar scalar	kg m2 s-1	[M][L]2

Moment of Inertia Theorems

Often the calculations for the M.O.I. of a body are not easy; fortunatley there are theorems which can simplify the calculation.

Theorem	Nomenclature	Equation
Superposition Principle for M.O.I. about any chosen Axis	$I_{\mathrm {net} }\,\!$ = Resultant M.O.I.	$I_{\mathrm {net} }=\sum _{j}I_{j}\,\!$
Parallel Axis Theorem	$M\,\!$ = Total mass of body $d\,\!$ = Perpendicular distance from an axis through the C.O.M. to another parallel axis $I_{\mathrm {com} }\,\!$ = M.O.I. about the axis through the C.O.M. $I\,\!$ = M.O.I. about the parallel axis	$I=I_{\mathrm {com} }+Mr^{2}\,\!$
Perpendicular Axis Theorem	i, j, k refer to M.O.I. about any three mutually perpendicular axes: the sum of M.O.I. about any two is the third.	$I_{\mathrm {k} }=I_{\mathrm {i} }+I_{\mathrm {j} }\,\!$

Galilean Transforms

The transformation law from one inertial frame (reference frame travelling at constant velocity - including zero) to another is the Galilean transform. It is only true for classical (Galilei-Newtonian) mechanics.

Unprimed quantites refer to position, velocity and acceleration in one frame F; primed quantites refer to position, velocity and acceleration in another frame F' moving at velocity V relative to F. Conversely F moves at velocity (—V) relative to F' .

Galilean Inertial Frames

$\mathbf {V} \,\!$ = Constant relative velocity between two frames F and F'. $\mathbf {r} ,\mathbf {v} ,\mathbf {a} \,\!$ = Position, velocity, acceleration as measured in frame F . $\mathbf {r} ',\mathbf {v} ',\mathbf {a} '\,\!$ = Position, velocity, acceleration as measured in frame F' .

Relative Position $\mathbf {r} '=\mathbf {r} +\mathbf {V} t\,\!$ Relative Velocity $\mathbf {v} '=\mathbf {v} +\mathbf {V} \,\!$ Equivalent Accelerations $\mathbf {a} '=\mathbf {a}$

Laws of Classical Mechanics

The following general approaches to classical mechanics are summarized below in the order of establishment. They are equivalent formulations, Newton's is very commonly used due to simplicity, but Hamilton's and Lagrange's equations are more general, and their range can extend into other branches of physics with suitable modifications.

Newton's Formulation (1687)

Force, acceleration, and the momentum rate of change are all equated neatly in Newton's Laws .

1st Law: A zero resultant force acting ON a body BY an external agent causes zero change in momentum. The effect is a constant momentum vector and therefore velocity (including zero). 2nd Law: A resultant force acting ON a body BY an external agent causes change in momentum. 3rd Law: Two bodies i and j mutually exert forces ON each other BY each other, when in contact.
The 1st law is a special case of the 2nd law. The laws summarized in two equations (rather than three where one is a corollary). One is an ordinary differential equation used to summarize the dynamics of the system, the other is an equivalance between any two agents in the system. Fij = force ON body i BY body j, Fij = force ON body j BY body i.	$\mathbf {F} ={\frac {\mathrm {d} \mathbf {p} }{\mathrm {d} t}}\,\!$ $\mathbf {F} _{\mathrm {ij} }=-\mathbf {F} _{\mathrm {ji} }\,\!$
In applications to a dynamical system of bodies the two equations (effectively) combine into one. pi = momentum of body i, and FE = resultant external force (due to any agent not part of system). Body i does not exert a force on itself.	${\frac {\mathrm {d} \mathbf {p} _{\mathrm {i} }}{\mathrm {d} t}}=\mathbf {F} _{E}+\sum _{\mathrm {i} \neq \mathrm {j} }\mathbf {F} _{\mathrm {ij} }\,\!$

Euler-Lagrange Formulation (1750s)

The generalized coordinates and generalized momenta of any classical dynamical system satisfy the Euler-Lagrange Equation, which is a set of (partial) differential equations describing the minimization of the system.	$p_{\alpha }={\frac {\partial L}{\partial {\dot {q}}_{\alpha }}}$ ${\dot {p}}_{\alpha }={\frac {\partial L}{\partial {q}_{\alpha }}}$
Written as a single equation:	${\frac {\mathrm {d} }{\mathrm {d} t}}\left({\frac {\partial L}{\partial {\dot {q}}_{\alpha }}}\right)=-{\frac {\partial L}{\partial q_{\alpha }}}$

Hamilton's Formulation (1833)

The generalized coordinates and generalized momenta of any classical dynamical system also satisfy Hamilton's equations , which are a set of (partial) differential equations describing the time development of the system.	${\frac {\partial \mathbf {p} }{\partial t}}=-{\frac {\partial H}{\partial \mathbf {q} }}$ ${\frac {\partial \mathbf {q} }{\partial t}}={\frac {\partial H}{\partial \mathbf {p} }}$
The Hamiltonian as a function of generalized coordinates and momenta has the general form:	$H=\left[\mathbf {q} (t),\mathbf {p} (t),t\right]$

— The value of the Hamiltonian H is the total energy of the dynamical system. For an isolated system, it generally equals the total kinetic T and potential energy V.

— Hamiltonians can be used to analyze energy changes of many classical systems; as diverse as the simplist one-body motion to complex many-body systems. They also apply in non-relativistic quantum mechanics; in the relativistic formulation the hamiltonian can be modified to be relativistic like many other quantities.

Derived Kinematic Quantities

For rotation the vectors are axial vectors (also known as pseudovectors), the direction is perpendicular to the plane of the position vector and tangential direction of rotation, and the sense of rotation is determined by a right hand screw system.

For the inclusion of the scalar angle of rotational position $\theta \,\!$, it is nessercary to include a normal vector $\mathbf {\hat {n}} \,\!$ to the plane containing and defined by the position vector and tangential direction of rotation, so that the vector equations to hold.

Using the basis vectors for polar coordinates, which are ${\boldsymbol {\hat {r}}},{\boldsymbol {\hat {\theta }}},{\boldsymbol {\hat {\phi }}}\,\!$, the unit normal is $\mathbf {\hat {n}} ={\boldsymbol {\hat {\theta }}}\times {\boldsymbol {\hat {r}}}\,\!$.

Quantity (Common Name/s)	(Common) Symbol/s	Defining Equation	SI Units	Dimension
Velocity	$\mathbf {v} \,\!$	$\mathbf {v} ={\frac {\mathrm {d} \mathbf {r} }{\mathrm {d} t}}\,\!$	m s-1	[L][T]-1
Acceleration	$\mathbf {a} \,\!$	$\mathbf {a} ={\frac {\mathrm {d} \mathbf {v} }{\mathrm {d} t}}={\frac {\mathrm {d} ^{2}\mathbf {v} }{\mathrm {d} t^{2}}}\,\!$	m s-2	[L][T]-2
Jerk	$\mathbf {j} \,\!$	$\mathbf {j} ={\frac {\mathrm {d} \mathbf {a} }{\mathrm {d} t}}={\frac {\mathrm {d} ^{3}\mathbf {v} }{\mathrm {d} t^{3}}}\,\!$	m s-3	[L][T]-3
Angular Velocity	${\boldsymbol {\omega }}\,\!$	${\boldsymbol {\omega }}=\mathbf {\hat {n}} {\frac {\mathrm {d} \theta }{\mathrm {d} t}}\,\!$	rad s-1	[T]-1
Angular Acceleration	${\boldsymbol {\alpha }}\,\!$	${\boldsymbol {\alpha }}={\frac {\mathrm {d} {\boldsymbol {\omega }}}{\mathrm {d} t}}=\mathbf {\hat {n}} {\frac {\mathrm {d} ^{2}\theta }{\mathrm {d} t^{2}}}\,\!$	rad s-2	[T]-2

By vector geometry it can be found that:

$\mathbf {v} ={\boldsymbol {\omega }}\times \mathbf {r} \,\!$

and hence the corollary using the above definitions:

$\mathbf {a} ={\boldsymbol {\alpha }}\times \mathbf {r} +{\boldsymbol {\omega }}\times \mathbf {v} \,\!$

Derived Dynamic Quantities

Quantity (Common Name/s)	(Common) Symbol/s	Defining Equation	SI Units	Dimension
Momentum	$\mathbf {p} \,\!$	$\mathbf {p} =m\mathbf {v} \,\!$	kg m s-1	[M][L][T]-1
Force	$\mathbf {F} \,\!$	$\mathbf {F} ={\frac {\mathrm {d} \mathbf {p} }{\mathrm {d} t}}\,\!$	N = kg m s-2	[M][L][T]-2
Impulse	$\Delta \mathbf {p} ,\mathbf {I} \,\!$	$\mathbf {I} =\Delta \mathbf {p} =\int _{t_{1}}^{t_{2}}\mathbf {F} \mathrm {d} t\,\!$	kg m s-1	[M][L][T]-1
Angular Momentum about a position point $\mathbf {R} \,\!$	$\mathbf {L} ,\mathbf {J} ,\mathbf {S} \,\!$	$\mathbf {L} =\left(\mathbf {r} -\mathbf {R} \right)\times \mathbf {p} \,\!$	kg m2 s-1	[M][L]2[T]-1
Total, Spin and Orbital Angular Momentum	$\mathbf {L} ,\mathbf {J} ,\mathbf {S} \,\!$	$\mathbf {L} _{\mathrm {total} }=\mathbf {L} _{\mathrm {spin} }+\mathbf {L} _{\mathrm {orbital} }\,\!$	kg m2 s-1	[M][L]2[T]-1
Moment of a Force about a position point $\mathbf {R} \,\!$, Torque	${\boldsymbol {\tau }},\mathbf {M} \,\!$	${\boldsymbol {\tau }}=\left(\mathbf {r} -\mathbf {R} \right)\times \mathbf {F} ={\frac {\mathrm {d} \mathbf {L} }{\mathrm {d} t}}\,\!$	N m = kg m2 s-2	[M][L]2[T]-2
Angular Impulse	$\Delta \mathbf {L} \,\!$ No common symbol	$\Delta \mathbf {L} =\int _{t_{1}}^{t_{2}}\mathbf {L} \mathrm {d} t\,\!$	kg m2 s-1	[M][L]2[T]-1
Coefficeint of Restitution	$e,\epsilon \,\!$	$e={\frac {\left|\mathbf {v} \right|_{\mathrm {separation} }}{\left|\mathbf {v} \right|_{\mathrm {approach} }}}\,\!$ usually $0\leqslant e\leqslant 1\,\!$ but it is possible that $e\geqslant 1\,\!$	Dimensionless	Dimensionless

Translational Collisions

For conservation of mass and momentum see Conservation and Continuity Equations.

Description	Nomenclature	Equation
Completley Inelastic Collision		$e=0\,\!$
Inelastic Collision		$0\leq \Delta T\leqslant \Delta T_{\mathrm {max} }\,\!$ $0\leq e\leq 1\,\!$
Elastic Collision		$\Delta T=0,e=1\,\!$
Superelastic/Explosive Collision		$e\geq 1\,\!$

General Planar Motion

The plane of motion is considered in a the cartesian x-y plane using basis vectors (i, j), or alternativley the polar plane containing the (r, θ) coordinates using the basis vectors $\left(\mathbf {\hat {r}} ,{\boldsymbol {\hat {\theta }}}\right)\,\!$.

For any object moving in any path $\mathbf {r} =\mathbf {r} \left(t\right)\,\!$ in a plane, the following are general kinematic and dynamic results :

Quantity	Nomenclature	Equation
Position	$r=r\left(t\right)\,\!$ = radial position component $\theta =\theta \left(t\right)\,\!$ = angular position component $R=R\left(t\right)\,\!$ = instantaneous radius of curvature at $\mathbf {r} \,\!$ on the curve $\mathbf {\hat {R}} \,\!$ = unit vector directed to centre of circle of curvature	$\mathbf {r} =\mathbf {r} \left(t\right)=r\mathbf {\hat {r}} +\theta {\hat {\boldsymbol {\theta }}}\,\!$
Velocity	$\omega \,\!$ = Instantaneous angular velocity	$\mathbf {v} =\mathbf {\hat {r}} {\frac {\mathrm {d} ^{2}r}{\mathrm {d} t^{2}}}+r\omega {\hat {\boldsymbol {\theta }}}\,\!$
Acceleration	$\alpha \,\!$ = Instantaneous angular acceleration	$\mathbf {a} =\left({\frac {\mathrm {d} ^{2}r}{\mathrm {d} t^{2}}}-r\omega ^{2}\right)\mathbf {\hat {r}} +\left(r\alpha +2\omega {\frac {\mathrm {d} r}{\mathrm {d} t}}\right){\hat {\boldsymbol {\theta }}}\,\!$
Centripetal Force	$\mathbf {m} =mR\mathbf {\hat {R}} \,\!$ = instananeous mass moment	$\mathbf {F} _{\bot }=-m\omega ^{2}R\mathbf {\hat {R}} \,\!$ $\mathbf {F} _{\bot }=-\omega ^{2}\mathbf {m} \,\!$

They can be readily derived by vector geometry and using kinematic/dynamic definitions, and prove to be very useful. Corollaries of momentum, angular momentum etc can immediatley follow by applying the definitions.

Common special cases are:

— the angular components are constant, so these represent equations of motion in a streight line — the radial components i.e. $\left|\mathbf {r} \right|\,\!$ is constant, representing circular motion, so these represent equations of motion in a rotating path (not neccersarily a circle, osscilations on an arc of a circle are possible) — $\omega \,\!$ and $\left|\mathbf {r} \right|\,\!$ are both constant, and $\alpha =0\,\!$, representing uniform circular motion — $\omega =0\,\!$ and ${\frac {\mathrm {d} ^{2}r}{\mathrm {d} t^{2}}}\,\!$ is constant, representing uniform acceleration in a streight line

Mechanical Energy

General Definitions

Quantity (Common Name/s)	(Common) Symbol/s	Defining Equation	SI Units	Dimension
Mechanical Work due to a Resultant Force	$W\,\!$	$W=\int _{C}\mathbf {F} \cdot \mathrm {d} \mathbf {r} \,\!$	J = N m = kg m2 s-2	[M][L]2[T]-2
Work done ON mechanical system, Work done BY	$W_{\mathrm {ON} },W_{\mathrm {BY} }\,\!$	$\Delta W_{\mathrm {ON} }=-\Delta W_{\mathrm {BY} }\,\!$	J = N m = kg m2 s-2	[M][L]2[T]-2
Potential Energy	$\phi ,\Phi ,U,V,E_{\mathrm {p} }\,\!$	$\Delta W=-\Delta V\,\!$	J = N m = kg m2 s-2	[M][L]2[T]-2
Mechanical Power	$P\,\!$	$P={\frac {\mathrm {d} E}{\mathrm {d} t}}\,\!$	W = J s-1	[M][L]2[T]-3
Lagrangian	$L\,\!$	$L=T-V\,\!$	J	[M][L]2[T]-2
Action	$S\,\!$	$S=\int L{\mathrm {d} t}\,\!$	J s	[M][L]2[T]-1

Energy Theorems and Principles

Work-Energy Equations

The change in translational and/or kinetic energy of a body is equal to the work done by a resultant force and/or torque acting on the body. The force/torque is exerted across a path C, this type of integration is a typical example of a line integral.

For formulae on energy conservation see Conservation and Continuity Equations.

Theorem/Principle	(Common) Equation
Work-Energy Theorem for Translation	$W=\Delta T=\int _{C}\mathbf {F} \cdot \mathrm {d} \mathbf {r} \,\!$
Work-Energy Theorem for Rotation	$W=\Delta T=\int _{C}{\left|{\boldsymbol {\tau }}\right|}{\mathrm {d} \theta }\,\!$
General Work-Energy Theorem	$W=\Delta T=\int _{C}\left(\mathbf {F} \cdot \mathrm {d} \mathbf {r} +{\left|{\boldsymbol {\tau }}\right|}{\mathrm {d} \theta }\right)\,\!$
Principle of Least Action A system always minimizes the action associated with all parts of the system.	Various minimized quantity formulations are: Maupertuis' Formulation $S=2\int T\mathrm {d} t\,\!$ Euler's Formulation $S=\int \left|\mathbf {p} \right|\mathrm {d} r\,\!$ Lagrangian Formulation $S=\int L\mathrm {d} t\,\!$

Potential Energy and Work

Every conservative force has an associated potential energy (often incorrectly termed as "potential", which is related to energy but not exactly the same quantity):

$\mathbf {F} =-\nabla W=\nabla E_{\mathrm {p} }\,\!$ $\int _{\mathbf {r} _{1}}^{\mathbf {r} _{2}}\mathbf {F} \mathrm {d} \cdot \mathbf {r} =-\Delta W=\Delta E_{\mathrm {p} }\,\!$

By following two principles a non-relative value to U can be consistently assigned:

— Wherever the force is zero, its potential energy is defined to be zero as well.

— Whenever the force does positive work, potential energy decreases (becomes more negative), and vice versa.

Useful Derived Equations

Description	(Common) Symbols	General Vector/Scalar Equation
Kinetic Energy	$T,E_{\mathrm {k} }\,\!$	$T={\frac {1}{2}}m{\left|\mathbf {v} \right|^{2}}={\frac {\left|\mathbf {p} \right|^{2}}{2m}}\,\!$
Angular Kinetic Energy	$T,E_{\mathrm {k} }\,\!$	$T={\frac {1}{2}}I{\left|{\boldsymbol {\omega }}\right|^{2}}={\frac {\left|\mathbf {L} \right|^{2}}{2I}}\,\!$
Total Kinetic Energy Sum of translational and rotational kinetic energy	$T,E_{\mathrm {k} }\,\!$	$T={\frac {1}{2}}m{\left|\mathbf {v} \right|^{2}}+{\frac {1}{2}}I{\left|{\boldsymbol {\omega }}\right|^{2}}={\frac {\left|\mathbf {p} \right|^{2}}{2m}}+{\frac {\left|\mathbf {L} \right|^{2}}{2I}}\,\!$
Mechanical Work due to a Resultant Torque	$W\,\!$	$W=\int _{C}{\left|{\boldsymbol {\tau }}\right|}{\mathrm {d} \theta }\,\!$
Total work done due to resultant forces and torques Sum of work due to translational and rotational motion	$W\,\!$	$W=\int _{C}\left(\mathbf {F} \cdot \mathrm {d} \mathbf {r} +\left|{\boldsymbol {\tau }}\right|\mathrm {d} \theta \right)\,\!$
Elastic Potential Energy	$E_{\mathrm {p} }\,\!$	$E_{\mathrm {p} }={\frac {1}{2}}kx^{2}={\frac {1}{2}}F\Delta \left(x^{2}\right)\,\!$
Power transfer by a resultant force	$P\,\!$	$P=\int _{C}\mathbf {F} \cdot {\mathrm {d} \mathbf {v} }\,\!$
Power transfer by a resultant torque	$P\,\!$	$P=\int _{C}{\boldsymbol {\tau }}\cdot {\mathrm {d} {\boldsymbol {\omega }}}\,\!$
Total power transfer due to resultant forces and torques Sum of power transfer due to translational and rotational motion	$P\,\!$	$P=\int _{C}\left(\mathbf {F} \cdot {\mathrm {d} \mathbf {v} }+{\boldsymbol {\tau }}\cdot {\mathrm {d} {\boldsymbol {\omega }}}\right)\,\!$

Transport Mechanics

Here $\mathbf {A} \,\!$ is a unit vector normal to the cross-section surface at the cross section considered.

Quantity (Common Name/s)	(Common) Symbol/s	Defining Equation	SI Units	Dimension
Flow Velocity Vector Field	$\mathbf {u} \,\!$	$\mathbf {u} =\mathbf {u} \left(x,t\right)\,\!$	m s-1	[L][T]-1
Mass Current	$I_{\mathrm {m} }\,\!$	$I_{\mathrm {m} }={\frac {\partial m}{\partial t}}\,\!$	kg s-1	[M][T]-1
Mass Current Density	$\mathbf {j} _{\mathrm {m} }\,\!$	$\mathbf {j} _{\mathrm {m} }=\mathbf {\hat {A}} {\frac {\partial I_{\mathrm {m} }}{\partial A}}=\mathbf {\hat {A}} {\frac {\partial ^{2}m}{\partial A\partial t}}\,\!$	kg m-2 s-1	[M][L]-2[T]-1
Momentum Current	$I_{\mathrm {p} }\,\!$	$I_{\mathrm {p} }={\frac {\partial \left|\mathbf {p} \right|}{\partial t}}\,\!$	kg m s-2	[M][L][T]-2
Momentum Current Density	$\mathbf {j} _{\mathrm {p} }\,\!$	$\mathbf {j} _{\mathrm {p} }={\frac {\partial I_{\mathrm {p} }}{\partial A}}={\frac {\partial ^{2}\mathbf {p} }{\partial A\partial t}}\,\!$	kg m s-2	[M][L][T]-2

Damping Parameters, Forces and Torques

Quantity (Common Name/s)	(Common) Symbol/s	Defining Equation	SI Units	Dimension
Spring Constant (Hooke's Law)	$k,K,\kappa ,k_{H}\,\!$	$k_{H}={\frac {\Delta F_{\bot }}{\Delta x_{\bot }}}\,\!$	N m-1	[M][T]-2
Damping Coefficient	$b\,\!$	$b=-{\frac {\Delta F_{\mathrm {d} }}{\Delta v_{\bot }}}\,\!$	N s m-1	[L][T]-1
Damping Force	$F_{\mathrm {d} }\,\!$		N	[M][L][T]-2
Damping Ratio	$\zeta \,\!$	$\zeta ={\frac {b}{b_{c}}}\,\!$	dimensionless	dimensionless
Logarithmic decrement	$\delta \,\!$	$\delta ={\frac {1}{n}}\ln {\frac {A_{0}}{A_{n}}}\,\!$ $A_{0}\,\!$ is any amplitude, $A_{n}\,\!$ is the amplitude n successive peaks later from $A_{0}\,\!$, where $A_{0}>A_{n}\,\!$	dimensionless	dimensionless
Torsion Constant	$\kappa \,\!$	$\kappa =-{\frac {\Delta \tau }{\Delta \theta }}\,\!$	N m rad-1	[M][L]2[T]-2
Damping Torque	$\tau _{\mathrm {d} }\,\!$		N m	[M][L]2[T]-2
Rotational Damping Coefficient	$\beta \,\!$	$\beta =-{\frac {\tau _{\mathrm {d} }}{\mathrm {d} \theta /\mathrm {d} t}}\,\!$	N m s rad-1	[M][L]2[T]-1