0:00:00.272,0:00:02.256 So, what are the consequences of something 0:00:02.256,0:00:05.113 being placed under pressure? Well, if I look 0:00:05.113,0:00:08.095 at this balloon, I can apply pressure to it by 0:00:08.095,0:00:12.694 exerting a force over its area. And when I do, 0:00:12.694,0:00:14.565 well, the balloon actually gets a little bit 0:00:14.565,0:00:17.930 smaller. The air inside the balloon gets a 0:00:17.930,0:00:20.348 little more densely packed together. And 0:00:20.348,0:00:24.597 in fact, this is exactly what happens on earth. 0:00:24.597,0:00:26.480 Out here, far away from the surface of the 0:00:26.480,0:00:29.761 earth, there are not very many air molecules. 0:00:29.761,0:00:31.606 This is a low pressure environment and 0:00:31.606,0:00:33.298 with nothing to weigh down on these air 0:00:33.298,0:00:35.849 molecules from above, they’re basically 0:00:35.849,0:00:38.832 free to play. They are free to move around. 0:00:38.832,0:00:40.811 Now below this outer layer of the 0:00:40.811,0:00:44.192 atmosphere, where all these air molecules 0:00:44.192,0:00:47.042 are sort of weighing on the atoms below it, 0:00:47.042,0:00:49.019 the molecules below it, and so these become 0:00:49.019,0:00:51.717 a little more densely packed. And as we go 0:00:51.717,0:00:53.387 even further down towards the surface of 0:00:53.387,0:00:57.223 the earth, where us humans tend to live, 0:00:57.223,0:00:59.503 the air gets even more densely packed. 0:00:59.503,0:01:01.248 And so we see that down near the surface 0:01:01.248,0:01:03.886 of the earth, where we have high pressure, 0:01:03.886,0:01:06.281 we also have a high density of air molecules. 0:01:06.281,0:01:08.299 And this high density of air molecules makes 0:01:08.299,0:01:11.752 us humans living at the surface very happy. 0:01:11.752,0:01:13.504 So I want to know, why do humans like high 0:01:13.504,0:01:15.362 pressure so much? Maybe the weight from 0:01:15.362,0:01:17.655 all that air above us keeps us from growing 0:01:17.655,0:01:20.025 too tall. Maybe air pollution tends to go to 0:01:20.025,0:01:22.504 regions of low pressure. Or maybe it means 0:01:22.504,0:01:24.774 that there’s lots of oxygen for us to breathe. 0:01:24.774,0:01:27.000 Go ahead and choose the best answer.