$1.$ Develop a model to explain why sucking up spaghetti will cause it to slap on one's face.

Hint: You can consider the force balance of a pendulum, where the length $\backslash ($ l $\backslash )$ is reduced during sucking. You may let $\backslash ($ l$($t$)=$l$\_\{0\}-$v t $\backslash ),$ where $\backslash ($ v $\backslash )$ is the velocity of sucking.