# Formulas, graphs & relations » Periodic relation

## Contents

1. General2. Formula

3. Graph

4. Amplitude, mean value and period

## 1. General

Graphs that repeat themselves continuously are called period graphs.

These graphs repeat with a certain time span which is called the period.

The number of periods during a unit of time is called the frequency.

Periodic relations appear with for example oscillations, waves and the height of the valve in you bicycle wheel.

## 2. Formula

Not all periodic graphs have a corresponding formula. In case they do, this formula is called a sinusoid. Such a formula is of the type `y` = `sin`

(`x`) or `y` = `cos`

(`x`).

Check sinusoid for more information about sinusoids.

You have to put your calculator in 'radian' mode when working with periodic formulas.

## 3. Graph

A periodic graph repeats it self. Below three examples.

This is the graph of `y` = `sin`

(`x`).

## 4. Amplitude, mean value and period

The *mean value* is the line where the graph fluctuates around.

The highest point of this graph is at `y` = 5 and the lowest point at `y` = 1,

so the mean value is `y` = (5 + 1) : 2 = 3.

The *amplitude* is the maximum deviation. The distance between the mean value and the highest or lowest point. For this graph that is 2.

The *period* is the regular time interval of the graph. For this graph it is 4.

Note:

In these graphs the relation is often between time and height.

In that case the mean value, amplitude and the period all have units.