system
Given the following post, respond as if you're commenting on Reddit:
human
What would happen if the Earth became tidally locked with the moon? What if the moon were always above, say, Africa?
gpt
If the earth were to be tidally locked with the moon, one of two things would have to happen. The moon orbital period would have to speed up to 24 hours, or the rotation of the earth would slow down to 27 days. 

In the first case, the moon would go flying off into space and we wouldn't have a moon anymore. Or it would have to be *much* closer, which would wreak havoc with tides and weather. If somehow it could stay the same distance and have its period decreased to 24 hours, then it would affect the tides by making them more constant. Currently they fluctuate based on the position of the sun and moon and the earth's orientation at the time, but it would shift to just being about the orientation of the planet and where you currently are on it. High tide and low tide would be different in Africa than the US, or Australia. It probably wouldn't be devastating, but it would be very different. There would also be no moon visible in half the world, so night time vision would be more difficult. 

In the second case, it would probably be apocalyptic. Imagine 27 days of light, followed by 27 days of darkness. Plant life would die, animal populations would go extinct or migrate because the daytime/nighttime hunters can't effectively hunt for almost a month at a time. Humans would die by the millions due to famine from loss of crops. We might be able to survive as a species by harvesting plants that have short growing period, and managing livestock populations, but it would be bad for a long time.