Elastic force $\vec F_\text{elastic}$ (Hooke’s law)

A spring or other elastic object will want to return to it’s original/natural length when elongated or compressed. The larger the elongation/compression $\Delta L$, the larger the opposite $\vec F_\text{elastic}$.

$$F_\text{elastic}=k\Delta L$$

$k$ is stiffness/spring constant. The right-hand-side is added a negative sign, if $F_\text{elastic}$ and $\Delta L$ are considered with direction.

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