已知命题 $p: \forall n \in N^*, n^2>\frac{1}{2} n-1$, 则命题 $p$ 的否定命题 为 ( )
A. $\exists {n} \in {N}^*, {n}^2 \leq \frac{1}{2} {n}-1$
B. $\forall {n} \in {N}^*, {n}^2 < \frac{1}{2} {n}-1$
C. $\forall {n} \in {N}^*, {n}^2 \leq \frac{1}{2^n-1}$
D. $\exists n \in N^*, n^2 < \frac{1}{2} {n}-1$