如图所示是用矿泉水瓶做的一个物理小实验，在瓶盖和瓶子侧壁各扎一个孔，图甲中用手堵住瓶盖上的孔，侧壁的孔中没有水流出；图乙中松开瓶盖上的小孔，侧壁的孔中有水流出，这个实验证明了的　____ 　存在．

    Hi! I'm Tony. I love 1! I always get up late on weekends. For breakfast, I only have 2. It's usually an apple. I have a big lunch. After lunch, I like to eat ice-cream. It 3 good. In the afternoon，I like to 4. I usually play basketball. Sometimes I swim. In the evening, I clean the house—I like 5rooms. I always go to bed late，at about 23: 00.

    But my sister doesn't like weekends. She has a job in a big store and she always works on weekends. She never goes out 6 her friends. She usually 7 home from work at 22:00. she 8 in bed after she takes a shower. But don't ask her 9 she reads. She always falls asleep (睡着) after 10 one or two pages (页).

解不等式 $\frac{x+1}{2}\ge 3\left(x-1\right)-4$ ．