"When does one use a one-tailed test or a two-tailed test"

In this week's Internet Resources: https://www.youtube.com/watch? Sal sets up an example of a one-tailed hypothesis test and two-tailed hypothesis test. Now create your own example showing when you would do a one-tailed test and when you would do a two-tailed test. Again this week I am not looking for an example from book. I want you to use your experience and interests to write a one-tailed hypothesis and a two tailed hypothesis. So here is an example of a two tailed test. On average, Americans and Europeans are about the same height. A one tailed test, American today are on average taller that than American were in 1900.