On the fifteenth day of the lunar calendar, the sun and the moon are on both sides of the earth, and the gravity vector to the earth should be equal to the difference between them, but why is there a

On the fifteenth day of the lunar calendar, the sun and the moon are on both sides of the earth, and the gravity vector to the earth should be equal to the difference between them, but why is there a spring tide on the earth at this time? You don't need to read the material I want to copy, because your question should be a mistake of physical common sense, and you won't be explained in the material.

Your misunderstanding is that you think that the resultant force on the object becomes smaller and the deformation of the object becomes smaller, right?

You said that on the fifteenth day of the lunar calendar, the gravity on the earth is the difference between the gravity of the sun and the moon, so the resultant force on the earth becomes smaller, so the tides should also become smaller.

In fact, tides are the manifestation of the deformation of the earth under the action of gravity, and the deformation of objects has nothing to do with the size of the resultant force. Even if the resultant force acting on an object is zero, it may be pulled in half by two forces of equal magnitude and opposite directions. The sun and the moon are on both sides of the earth, and gravity can only change the shape of the earth more.

You got it?