Forces Equilibrium vs. Dynamic Tides
Forces that create tides Earth-sun and Earth-moon systems Example of swinging bucket Centripetal forces Gravitational forces Resultant forces
Equilibrium tides Water covered earth (no continents) No friction on earth Drawings of earth-moon-sun system Note position of bulges Note alignment of earth-moon vs. earth-sun
Spring vs. Neap Tides
Dynamic tides Earth is not ideal Orbits are ellipses not circles Basins have variable shapes Earth is tipped on its axis as are other planetary bodies
Varieties of tides Diurnal tides: 1 high, 1 low per day Semi-diurnal tides: 2 highs, 2 lows per day Mixed tides: 2 highs, 2 lows per day, but of unequal heights (one example)
Consider highs and lows in each tidal day
Tides in inlets No swimming signs Tidal currents moving through inlet ebb tidal current flood tidal current slack water
Tide height Current speed
Tidal currents in rivers Tidal bores: strong river current meets strong flood tidal current and creates a wave!
Approaching tidal bore on river in Nova Scotia Photo by MS Bollinger