cinématique

Kinematics focuses on three main quantities:

• Average velocity: $\vec{v}{avg} = \frac{\Delta \vec{r}}{\Delta t} = \frac{\vec{r}{final} - \vec{r}{initial}}{t{final} - t_{initial}}$
• Instantaneous velocity: $\vec{v}(t) = \frac{d\vec{r}}{dt}$ (the derivative of position with respect to time). Its magnitude is called speed.

When moving from 2D to 3D kinematics, you're essentially adding a z-component to all your vector quantities. Everything you learned about position, velocity, and acceleration in 2D still applies, but now in three orthogonal directions.

In a Cartesian coordinate system (your standard x, y, z axes), the position vector $\vec{r}(t)$ of a point P at time $t$ is:
$\vec{r}(t) = x(t)\vec{i} + y(t)\vec{j} + z(t)\vec{k}$

Ces trois concepts sont liés et décrivent entièrement le mouvement d'un objet.

1. Position initiale : Tu es au feu rouge, on va dire à x = 0 mètres.
2. Tu commences à pédaler. Au bout de 2 secondes, ta vitesse est de 5 m/s.
3. Tu maintiens cette vitesse pendant 3 secondes supplémentaires.
4. Puis, tu décides d'accélérer et, en 1 seconde, ta vitesse passe de 5 m/s à 8 m/s.