In one cubic centimeter of air there are about 2, 000 ions.
一立方厘米的空气中约有2000个离子。
2
If you take a pebble with a radius of about one centimeter and you throw it off a high building, it will reach a speed which will not exceed 75 miles per hour because of the air drag.
如果拿一个半径是，1厘米的小卵石，从高楼上扔下去，它的速度因为空气阻力，不过超过每小时75英里。
3
According to the mensuration, air negative oxygen ion 14700 per cubic centimeter, chengdu, Beijing and 200-220 times.