# Definition:Orbit (Physics)

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*This page is about Orbit in the context of Physics. For other uses, see Orbit.*

## Definition

Let $A$ and $B$ be bodies in space.

The **orbit** of $A$ around $B$ is the path taken by $A$ as it travels around $B$ under the influence of the force acting between $A$ and $B$.

### Period of Orbit

The **period** of the orbit is the length of time it takes for $A$ to travel once around $B$ and return to its original position.

### Radius of Orbit

Let $\mathbf r$ be the position vector of the center of mass of $A$ with respect to the center of mass of $B$ at a particular point in time.

The **radius** of the orbit of $A$ around $B$ is defined as:

- the position vector $\mathbf r$

or

- the length of $\mathbf r$.

Context will determine which is meant.

## Also see

## Sources

- 1998: David Nelson:
*The Penguin Dictionary of Mathematics*(2nd ed.) ... (previous) ... (next):**orbit**:**1.** - 2008: David Nelson:
*The Penguin Dictionary of Mathematics*(4th ed.) ... (previous) ... (next):**orbit**:**1.** - 2014: Christopher Clapham and James Nicholson:
*The Concise Oxford Dictionary of Mathematics*(5th ed.) ... (previous) ... (next):**orbit**