# Relative velocity and closing speed

DevFeed: [Relative velocity and closing speed](<https://devfeed.tech/articles/relative-velocity-and-closing-speed-35144.md>)

Original publisher: [Read original article](<https://eli.thegreenplace.net/2026/relative-velocity-and-closing-speed/>)

Author: Eli Bendersky

Published: 2026-08-04T03:01:00Z

Content type: tutorial

Language: en

Sources: [Eli Bendersky](<https://devfeed.tech/sources/eli-bendersky.md>)

Topics: [Simulation](<https://devfeed.tech/topics/simulation.md>), [Game engine](<https://devfeed.tech/topics/game-engine.md>), [3D](<https://devfeed.tech/topics/3d.md>)

Tags: [3d](<https://devfeed.tech/tags/3d.md>), [game](<https://devfeed.tech/tags/game.md>), [math](<https://devfeed.tech/tags/math.md>), [misc](<https://devfeed.tech/tags/misc.md>), [physics](<https://devfeed.tech/tags/physics.md>)

## AI overview

A tutorial on closing speed, defined as the normal component of the relative velocity between two objects. It explains vector projection, the role of the connecting line between the objects, and how the sign indicates whether they are approaching or separating.

## Source excerpt

In Physics simulations or game engines it's sometimes useful to determine the speed with which two objects are approaching each other. This post will discuss the concept of closing speed, which is the normal component of the relative velocity of two objects. Relative velocity and its components Suppose we ...