WEBVTT 00:00:00.062 --> 00:00:02.764 This is College physics Answers with Shaun Dychko. 00:00:03.146 --> 00:00:07.306 The pressure inside a balloon we're told is one and a half centimeters of water. 00:00:07.786 --> 00:00:11.653 So that means the pressure will raise water in a column up 00:00:11.813 --> 00:00:15.813 one and a half centimeters in an open tube manometer. 00:00:16.764 --> 00:00:21.671 But anyway, we're going to convert that into Pascals by using this formula here. 00:00:23.280 --> 00:00:32.417 So the pressure in a sphere due to surface tension of a liquid 00:00:32.417 --> 00:00:36.080 is four times the surface tension divided by the radius of the sphere. 00:00:36.568 --> 00:00:41.813 We can solve this for surface tension by multiplying both sides by r over four. 00:00:44.400 --> 00:00:46.515 We get gamma is P r over four. 00:00:47.724 --> 00:00:52.168 The pressure is going to be the pressure due to this column of water 00:00:52.168 --> 00:00:54.560 which is the density of water times g times its height 00:00:54.844 --> 00:00:56.640 and so we substitute that in for the pressure. 00:00:57.431 --> 00:01:01.982 So we have the effective surface tension of the balloon 00:01:02.115 --> 00:01:04.124 which is sort of the stretchiness of the rubber, 00:01:04.897 --> 00:01:10.017 is the one times ten to the three kilograms per cubic meter density of water 00:01:10.260 --> 00:01:14.328 times 9.81 newtons per kilogram, times one and a half centimeters 00:01:14.328 --> 00:01:16.115 which is times ten to the minus two meters, 00:01:16.737 --> 00:01:18.897 times ten times ten to the minus two meters height, 00:01:18.897 --> 00:01:22.195 sorry radius of the balloon, and divide that by four. 00:01:22.195 --> 00:01:25.066 You get 3.68 newtons per meter. 00:01:25.440 --> 00:01:29.306 Now this number is a lot more than the surface tensions 00:01:29.306 --> 00:01:31.502 listed in the data table given to us 00:01:31.502 --> 00:01:35.715 and we expect that because in the data table 00:01:35.715 --> 00:01:38.328 we're dealing with surface tensions of liquids 00:01:38.471 --> 00:01:42.977 whereas this is an elastic soli\d and so we expect the number to be bigger.