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[NOTES/CM-08014] Active and Passive Rotations

The active and passive view of rotations are defined and relationship between them is described.

 

[NOTES/CM-08012] Matrices for Rotations about Coordinate Axes

The rotation matrices for rotations about the three axes are listed.

[NOTES/CM-08011] Rotations about a fixed axis

Rotations about a fixed axis form a one parameter subgroup of  rotations.

[NOTES/CM-08010] Motion in Frames with Linear Acceleration

The equations of motion in a linearly accelerated are are derived and an expression for pseudo force is obtained.

[NOTES/CM-08009] Centrifugal force --- Effect of Earth's Rotation

The effect of Coriolis force on the force acting on a body on the earth is computed at the poles, equator and at a general point. he banking of railway tracks and of roads is briefly discussed.

[CHAT/CM-08007] Let's Talk --- Fundamental Interactions

A short discussion of pseudo forces and fundamental interactions is given.

[NOTES/CM-08004] Equation of Motion in Non Inertial Frames

 We derive an expression for Lagrangian for motion of a charged particle in a rotating frame, It is shown that the equation of motion can be written as

\begin{eqnarray} m\ddot{\vec{x}}=\vec{F_{e}}-2m\vec{\omega}\times{\dot{\vec{x}}}-m\vec{\omega} \times(\vec{\omega}\times\vec{x}) \end{eqnarray} where \(\vec {F}_e\) is the external force. As seen from the rotating frame, the particle moves as if it is under additional forces

  • $-2m\vec{\omega}\times{\dot{\vec{x}}}$ is called Coriolis force
  • $-m\vec{\omega}\times(\vec{\omega}\times\vec{x})$ is known as centrifugal force 

 

[NOTES/CM-08008] Proper Rotations and $SO(3)$

The definition and properties of proper rotations are presented.

[NOTES/CM-08006] Axis Angle Parametrization of Rotation Matrix

A closed form expression for rotation matrix is derived for rotations about an axis by a specified angle \(\theta\).

\begin{equation}
R_{\hat{n}}(\theta)=\widehat {Id}-\sin (\theta) (\hat{n}\cdot \vec{I})+(1-\cos \theta)(\hat{n}\cdot\vec{I})^{2}
\end{equation}Here  \(\widehat{Id} \) is the identity matrix. and \(\vec{I}=(I_1,I_2,I_3)\) is given by 
\begin{equation} I_1=\left[\begin{array}{clc} 0 &0 &0\\ 0 &0 &-1\\ 0 &1 &0 \end{array}\right],I_2=\left[\begin{array}{clc} 0 &0 &1\\ 0 &0 &0\\ -1 &0 &0 \end{array}\right],I_3=\left[\begin{array}{clc} 0 &-1 &0\\ 1 &0 &-1\\ 0 &1 &0 \end{array}\right] \end{equation}. 

Also the components of the position vector a point transform a

\begin{equation} {\vec{x}}\Prime=(\hat{n}\cdot{\vec{x}})\hat{n}+\cos\theta\big(\vec{x}-(\vec{x}\cdot\vec{n})\hat{n}\big)-\sin\theta (\hat{n}\times \vec{x})\end{equation}

 

[NOTES/CM-08005] Finite Rotations of Vectors about an Arbitrary Axis

Using geometrical arguments, we will derive the result \begin{equation}\vec{A}^\prime = \vec{A} - (\hat{n}\times\vec{A})\, \sin\alpha + \hat{n}\times (\hat{n}\times\vec{A})\, (1-\cos\alpha ) \end{equation}between components of vectors related by a rotation by and angle \(\theta\) about an axis \(\hat n\).

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