Weather Talk: Here's what causes tides that have been in the news
Tides have been in the news lately because the timing of high tides has been a factor in coastal flooding during the recent hurricanes. Tides are caused by differential gravity. The moon exerts a gravitational force upon the Earth, but because this force is related to distance, it is slightly stronger on the side of the Earth facing the moon and slightly weaker on the away side. The solid body of Earth is largely unaffected by this difference. However, the ocean is a fluid. The part of the ocean closest to the moon is pulled more than the solid Earth and the part of the ocean opposite the moon is pulled less. This is why there are two high tides and two low tides each day on the ocean. Lakes do not have noticeable tides because the difference in the gravitational pull from one side of a lake to the other is negligible. Likewise, a human body is far too small to be affected by tides.