A one-eighth scale model of a car is to be tested in a wind tunnel. If the air velocity over the car is $16 \mathrm{~m} / \mathrm{s}$, what should be the air velocity $\text{(in $\mathrm{m} / \mathrm{s}$)}$ in the wind tunnel in order to achieve similarity between the model and the prototype?
- $2$
- $16$
- $64$
- $128$
