1 00:00:00,520 --> 00:00:03,280 Speaker 1: Welcome to brain Stuff from house stuff works dot com 2 00:00:03,600 --> 00:00:08,039 Speaker 1: where smart happens. Hi Am Marshall Brain With today's question 3 00:00:08,520 --> 00:00:12,399 Speaker 1: how much does planet Earth weigh? It would be more 4 00:00:12,520 --> 00:00:15,560 Speaker 1: proper to ask what is the mass of Planet Earth? 5 00:00:15,880 --> 00:00:19,759 Speaker 1: The quick answer to that is approximately six times ten. 6 00:00:19,840 --> 00:00:25,360 Speaker 1: To them, it weighs a lot. The interesting sub question 7 00:00:25,560 --> 00:00:28,720 Speaker 1: is how did anyone figure that out? It's not like 8 00:00:28,760 --> 00:00:31,920 Speaker 1: the planet steps onto a scale each morning before it 9 00:00:31,960 --> 00:00:35,320 Speaker 1: takes a shower. It turns out that you can calculate 10 00:00:35,360 --> 00:00:38,440 Speaker 1: the mass of something if you know the magnitude of 11 00:00:38,479 --> 00:00:43,920 Speaker 1: its gravitational pull. Any two masses have a gravitational attraction 12 00:00:44,000 --> 00:00:47,120 Speaker 1: for one another. If you put two bowling balls near 13 00:00:47,159 --> 00:00:51,280 Speaker 1: each other, they will attract one another Gravitationally, the attraction 14 00:00:51,520 --> 00:00:55,480 Speaker 1: is extremely slight, but if your instruments are sensitive enough, 15 00:00:55,520 --> 00:00:59,160 Speaker 1: you can measure that gravitational attraction that two bowling balls 16 00:00:59,240 --> 00:01:02,280 Speaker 1: have on one an other. From that measurement, you could 17 00:01:02,360 --> 00:01:05,399 Speaker 1: determine the mass of the two objects. The same is 18 00:01:05,400 --> 00:01:08,319 Speaker 1: true for two golf balls, but the attraction is even 19 00:01:08,360 --> 00:01:12,520 Speaker 1: slighter because the amount of gravitational force depends on the 20 00:01:12,560 --> 00:01:17,280 Speaker 1: mass of the objects. Newton showed that for spherical objects 21 00:01:17,400 --> 00:01:20,160 Speaker 1: you can make the simplifying assumption that all of the 22 00:01:20,240 --> 00:01:23,960 Speaker 1: objects mass is concentrated at the center of the sphere. 23 00:01:24,319 --> 00:01:27,440 Speaker 1: He then came up with an equation that expresses the 24 00:01:27,480 --> 00:01:31,800 Speaker 1: gravitational attraction that two spherical objects have on one another. 25 00:01:32,319 --> 00:01:37,440 Speaker 1: It's force equals the gravitational constant times the mass of 26 00:01:37,440 --> 00:01:40,240 Speaker 1: the first object times the mass of the second object 27 00:01:40,680 --> 00:01:44,920 Speaker 1: over the distance between the two objects squared. Assume that 28 00:01:45,040 --> 00:01:47,640 Speaker 1: Earth is one of the masses and that a one 29 00:01:47,720 --> 00:01:51,640 Speaker 1: kilogram sphere is the other. The force between them is 30 00:01:51,840 --> 00:01:55,640 Speaker 1: nine point eight kilogram meters per second squared. We can 31 00:01:55,680 --> 00:01:59,320 Speaker 1: calculate this force by dropping the one ram sphere and 32 00:01:59,440 --> 00:02:03,720 Speaker 1: measuring acceleration that the Earth's gravitational field applies to it, 33 00:02:03,800 --> 00:02:07,400 Speaker 1: which is nine eight ms per second squared. The radius 34 00:02:07,440 --> 00:02:11,040 Speaker 1: of the Earth is six million, four hundred thousand meters. 35 00:02:11,400 --> 00:02:14,160 Speaker 1: If you plug all these values in and solve for 36 00:02:14,400 --> 00:02:16,919 Speaker 1: M one, you find that the mass of the Earth 37 00:02:17,160 --> 00:02:21,800 Speaker 1: is six times ten to Do you have any ideas 38 00:02:21,880 --> 00:02:25,000 Speaker 1: or suggestions for this podcast? If so, please send me 39 00:02:25,040 --> 00:02:28,200 Speaker 1: an email at podcast at how stuff works dot com. 40 00:02:28,360 --> 00:02:30,640 Speaker 1: For more on this and thousands of other topics, go 41 00:02:30,720 --> 00:02:33,519 Speaker 1: to how stuff works dot com and be sure to 42 00:02:33,600 --> 00:02:35,840 Speaker 1: check out the brain Stuff blog on the how stuff 43 00:02:35,840 --> 00:02:37,160 Speaker 1: works dot com home page.