Why do the sun and moon produce considerable tides in the earths oceans but barely any in lakes?

Question

I need help on my physical science challenge.

Answer 1

The oceans are much larger than lakes. Every molecule of water is attracted  by the moon and the sun. The sun is more massive, but much farther away than the moon, so the main factor is the moon with a sun effect as well. The equation is Newton's gravitational equation, F = GM₁M₂/R² where the two masses M are the mass of the moon and the earth or the particle of water (moon effect only now for simplicity, ignore sun), G the gravitational constant, and R the distance between the earth and the moon. The acceleration of a particle on the earth is F/m by the equation for acceleration. The acceleration of the molecule of water is therefore related to the mass of the moon as the mass of the water divides out. The water molecules are so small compared to the moon that the net effect is all in movement toward the moon. There are more complicated equations related to the acceleration on both the earth and the water, but for your question these aren't needed.

 

The oceans have large masses and large numbers of molecules of water. While the Mediterranean is a bit bigger than Lake Superior, even the Great Lakes are much smaller in size than any one of the great oceans, such as the Atlantic. Depending on the depth of the sea near the shores, one will see greater or lesser effects of the tides. The moon, as it travels around the earth, attracts the water molecules. Due to inertia there is a lag as these molecules are attracted toward the moon, so that the water moves and causes a bulge, that is, the tide. Because the earth is moving, it appears that the bulge is moving toward the coasts, but it is the earth that is moving underneath the water. The earth's crust is also attracted, but it cannot move like water can, so we don't see these effects. The Great Lakes do have a minimal tide, about 2 inches maximum. Because the lakes have numerous other working factors, such as wind and barometric pressure, and these effects are much larger than the tidal effect, the lakes appear to be non-tidal. They just don't have enough water and don't cover enough land area to produce a visible tidal effect.

 

The sun's effect is about half that of the moon. When both coincide, we get larger tides, called Spring Tides.

When hurricanes hit, if their weather-related effects (whipping up the water) occur at high tide, the effects are much greater than they might have been.

 

Hope this helps!

 

Dorene O.