# Definition:Kinetic Energy of Classical Particle

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## Definition

Let $\MM$ be an $n$-dimensional Euclidean manifold.

Let $P$ be a particle with an inertial mass $m_i$.

Let $t$ be the time variable of $P$.

Suppose the position of $P$ is a real differentiable $n$-dimensional vector-valued mapping $\mathbf x = \map {\mathbf x} t$.

Then the **kinetic energy** of a **classical particle** $P$ is:

- $T = \dfrac {m_i} 2 \paren {\dfrac {\d \mathbf x} {\d t} }^2$

where $\paren {\dfrac {\d \mathbf x} {\d t} }^2$ is the dot product of the vector $\dfrac {\d \mathbf x} {\d t}$ with itself.

## Sources

- 1963: I.M. Gelfand and S.V. Fomin:
*Calculus of Variations*... (previous) ... (next): $\S 4.21$: The Principle of Least Action