Earth revolves around the sun and at the same time rotates on its axis. Revolutions cause change of season and calendar year while rotation causes day and night. If Earth for some reason stopped rotating we would observe six months of day and 6 months of night.
The problems would certainly increase when you are exposed to Sun for such a long time. These areas would become hotter and this would impact the crops as well. Similarly is for the other half which would have the night for 6 months till Earth revolves and this half of the Earth starts facing the Sun. Trees need sunlight for photosynthesis, with lack or excessive sunlight trees would get majorly impacted and break the food chain. There are huge chances of food scarcity.
The places which are not directly facing the Sun, however, would have some light reaching them would be the ideal places for people to live. Temperature would be moderate and there are chances for crops to survive in these locations. Major populations would prefer migrating to these places and this would cause a population explosion. Resources available in these areas would be hugely exploited and we would soon run out of stock.
The rotation of Earth creates a centrifugal force which is the cause of the bulge at the equator. This centrifugal force is the key to holding water at the center of the globe. When earth would stop rotating, centrifugal force would be lost. It is believed that this would cause a movement of water from the equator to the poles. With a huge amount of water movement, many countries which are located towards the poles will get submerged under water. Population living in these areas would have to be moved to areas near the equator. There would be a large mass of land left at the center which would be consumed by people to live.
Earth’s magnetic field would be lost. It is predicted that the earth's magnetic field is created by the difference in rotation between the core and the outer surface of the earth. When the earth's rotation would stop, it would also bring an end to this magnetic field as well.
Few researchers believe that it would be a massive destruction when the earth would stop. They say this on the basis of momentum with which we are moving along with the Earth. We don’t feel it as we are rotating along with it. When it would stop suddenly everything would move sideways from the equator with a force.
It would be like the sudden jerk which we receive when we stop a fast-moving vehicle. The only difference here is that the earth rotates at a very high speed; we would not fall in the space however high magnitude of earthquakes or huge destructive tides could be experienced.