3.10: Kinetic energy
( \newcommand{\kernel}{\mathrm{null}\,}\)
We remind ourselves that we are discussing particles, and that all kinetic energy is translational kinetic energy.
Notation:
- T_{C} = kinetic energy with respect to the centre of mass C.
- T = kinetic energy with respect to the origin O.
T = T_{C} + \frac{1}{2}M\overline{v}^{2}\tag{3.10.1}\label{eq:3.10.1}
Thus:
T = \frac{1}{2}\sum m_{i}{v}^{2}_{i} = \frac{1}{2} \sum m_{i} ({\bf v} ^{\prime}_{i} + \overline{{\bf v} })\cdot ({\bf v} ^{\prime}_{i} + \overline{{\bf v} })
= \frac{1}{2}\sum m{v}^{\prime 2}_{i} \times \overline{{\bf v} } \sum m{{\bf v} }^{\prime}_{i} + \frac{1}{2} v^{-2} \sum m_{i}.
\therefore \qquad T = T_{C} + \frac{1}{2}M\overline{v}^{2} .
If \overline{{\bf v} } = 0, T = T_{C}. (Think about what this means.)
Corollary: For a non-rotating rigid body, T_{C} = 0, and therefore T = \frac{1}{2}M\overline{v}^{2}
(Think about what this means.)