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Physics LibreTexts

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.
Theorem:

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} .

Corollary:

If \overline{{\bf v} } = 0, T = T_{C}. (Think about what this means.)

Corollary:

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.)


This page titled 3.10: Kinetic energy is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Jeremy Tatum via source content that was edited to the style and standards of the LibreTexts platform.

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