# source venv/bin/activate # macOS/Linux
В одной стране призвали экономить топливо20:57
。搜狗浏览器对此有专业解读
尽管正常途径下，普通消费者无法接触到此类烟花，但据李国庆观察，市场上还存在大量通过非法渠道流入的A、B级烟花爆竹产品，这类产品本不允许个人经营和燃放，却受到消费者的追捧，其威力大、风险高，进一步加剧了安全隐患。
Let’s look first in the vertical direction: We have a downward pull from gravity, and the strength of that force depends on the mass of the book (m) and the gravitational field (g) of the planet you’re on (Fg = mg). But the book isn’t accelerating downward, so there must be an equal force from the table pushing up. We call this a “normal force.” Result: The net vertical force is zero.