Ocean Tides: Gravitational Forces of the Moon and Sun

Why this matters

The Bay of Fundy pushes its tidal range past 15 meters, funneling the same gravitational pull that raises tides everywhere else into something dramatic enough to reshape the coastline twice a day. That range only makes sense once students see why the Moon's pull creates two bulges of water on opposite sides of Earth at once.

My students usually expect the bigger Sun to do most of the work raising tides, and it catches them off guard that the Moon's pull already sets up the two bulges before the Sun's pull ever gets added in. Spring and neap tides click once they see the Sun's pull adding to, or canceling, the Moon's.

From one teacher to another

Twice a day, coastlines rise and fall in a rhythm set by the gravitational pull of the Moon and the Sun. The reading breaks down how the Moon's pull creates two bulges of water on opposite sides of Earth, and how the Sun's added pull produces stronger spring tides or weaker neap tides depending on alignment. The case study on the Bay of Fundy explains how a funnel-shaped bay can amplify tidal range past 15 meters, creating both tourism draws and challenges for local fishermen.