# Frames and FPS: pictures over time

[Concepts explained](README.md)

A **frame** is one picture in an animation. Showing a series of slightly different pictures can create the appearance of movement. **FPS** means *frames per second*: how many frames are shown in one second.

A flipbook makes a useful model. Each page is a frame; turning the pages faster changes how quickly you see them.

## Time per frame

One second contains 1,000 milliseconds. At 25 frames per second, the time available for each frame is 1 / 25 second, or 0.04 seconds: 40 milliseconds.

```pliro
# language: en
let framesPerSecond = 25
say 1 / framesPerSecond
```

This prints `0.04`. It calculates an interval; it does not turn on an automatic animation system.

## Waiting is not a speed guarantee

A loop also spends time calculating and drawing. Adding `wait(0.04)` after that work can make each round take longer than 0.04 seconds. The window's display rate can differ from the program's update rate too.

An **update** changes game state, such as a position. A **render** draws that state. A sprite's animation pose may change less often than its position. Keeping these jobs separate helps explain why a character can move smoothly while reusing the same picture.

Try a paper flipbook at two different speeds. Does increasing the page-turn speed add any new drawings?

[Animation](../guides/animation.md) · [Event timing](event-loop.md)