Rotations
Space and Body Space coordinates are an inertial system. Fixed in spaceFixed in space Body coordinates are a non- inertial system. Move with rigid body x1x1 x2x2 x3x3 x1x1 x2x2 x3x3
Matrix Form A linear transformation connects the two coordinate systems. The rotation can be expressed as a matrix. Use matrix operationsUse matrix operations Distance must be preserved. Matrix is orthogonalMatrix is orthogonal Product is symmetricProduct is symmetric Must have three free parametersMust have three free parameters x1x1 x2x2 x3x3
Axis of Rotation An orthogonal 3 x 3 matrix will have one real eigenvalue. Real parameters Cubic equation in s The eigenvalue is unity. Matrix leaves length unchanged The eigenvector is the axis of rotation. x1x1 x2x2 x3x3 +1 for right handedness
Single Rotation The eigenvector equation gives the axis of rotation. Eigenvalue = 1Eigenvalue = 1 The trace of the rotation matrix is related to the angle. Angle of rotation Angle of rotation Trace independent of coordinate systemTrace independent of coordinate system
Rotating Vector A fixed point on a rotating body is associated with a fixed vector. Vector z is a displacement Fixed in the body system Differentiate to find the rotated vector. x1x1 x2x2 x3x3
Angular Velocity Matrix The velocity vector can be found from the rotation. The matrix is related to the time derivative of the rotation. Antisymmetric matrixAntisymmetric matrix Equivalent to angular velocity vectorEquivalent to angular velocity vector
Matching Terms The terms in the matrix correspond to the components of the angular velocity vector. The angular velocity is related to the S matrix.
Body Rotation The angular velocity can also be expressed in the body frame. Body version of matrixBody version of matrix x1x1 x2x2 x3x3