I’ll admit it – besides “knowing” that tides were caused by the moon’s gravitational pull, I had no idea why tides existed. A science teacher training class forced me to confront this ignorance starting with the simple question – if the moon’s gravitational pull causes tides, why do we have two high tides and two low tides in a day? (the moon’s orbit around the earth takes roughly a month, so tides should basically be dictated by the earth’s rotation – i.e. take 24 hours to go from one high tide to the next).
Digging deeper into the matter, I became pretty frustrated – online resources typically introduced another force (centrifugal force) to explain why the ocean “bulges” towards the moon (and sun, which is another layer in this topic), but it was hard to develop an intuition of how this all works together from the material that I found. Fortunately, people like Ingo Berg exist. His website has an application that finally helped me visualize the forces that shape tides – it might also help your students who need to construct visuals to understand concepts.
