---
title: 'Wave or corpuscules? or both ...'
media_order: 'corpuscule-trajectory-tennis-ball.jpg,refraction-cuillere.jpg,sky-light-rays-827.jpg,wave-corpuscular-nature-of-light-experiment1.gif,waves-interferences-surface-water-827-496.jpg,reflexion-statuette.jpg'
---

### How do we understand our physical world ?

* We interpret the world with two intuitive concepts that are in our mind mutually exclusive : the concept of corpuscule and the concept of wave

##### Localized corpuscules with trajectories

In our mind, a **corpuscule** is *localized in space*, and **At each instant** can be characterized by :
* a *position in space*
* a *speed*
* an *acceleration*

It carries :
* *matter*
* *energy*
* *momentum*

Between two instants, its movement describes a *trajectory* : continuous set of positions followed by the corpuscule between these two instants.

The **behavior of a corpuscule** *at human scale*, and **their interactions with each other**, is well described and predicted by *classical mechanics*.

* **classical mechanics** = **Newton's mechanics** = **point mechanics**

![](corpuscule-trajectory-tennis-ball.jpg)

##### Waves that interfer to each other

In our mind, a **wave**  is *not localized in space*, and **in the whole time** can be characterized by :
* a *frequency*
* a *velocity*
* frequency + velocity $\Longrightarrow$ a *wavelength*
* an *amplitude*
* a *polarization* (depending of wave type)

A wave 
* *does not carry matter*
* *carries energy*

**Several waves** interfer with each other, giving rise to *interferences*

A wave **passing through a small aperture** (of size of the order or small than wavelength) is *diffracted*

![](waves-interferences-surface-water-827-496.jpg)


### How light behaves ?

![](wave-corpuscular-nature-of-light-experiment1.gif)

A modern Youngs'type experiment :
behavior of light passing through two slits and 
The light emerging from a double slit, whose the width (of each slot) and the spacing (between the two slots) are sufficiently small, 


### What optical phenomena do we observe in everyday life ?

* The **light** describes in *straight lines in air*.<br>
$\Longrightarrow$ concept of *light ray*

![](sky-light-rays-827.jpg)

##### Refraction phenomenon

* The light seems to *change direction from water to air*.<br>
![](refraction-cuillere.jpg)

* can be d

##### Reflection phenomenon

![](reflexion-statuette.jpg)

