## Newton's Law of Restitution - Imagine a ball dropped vertically onto a hard horizontal surface - Suppose it has velocity $u$ immediately before it hits the surface, and after the bounce it has velocity $v$ - It is found that $v=-eu$ where $e$ is a constant independent of $u$ and $v$ - The constant $e$ is called the *coefficient of restitution* - Imagine a ball is dropped at angle in a vertical direction. The object will have velocity in horizontal and vertical components. - So before the collision it has velocity with components $u_{x}$ and $u_{y}$, after the collision it will gave components $v_x$ and $v_{y}$ - Each component of the collision may have it's own value of $e$ (as $e_{x}$ and $e_{y}$) Let's assume $e_{x}=1$ and $e_{y}=e$. Then, the velocity component perpendicular to the surface is changed, so $v_{y}=eu_{y}$ and $v_{x}=u_{x}$