Why do we have high and low tides (sea level changes)?
The moon, being much nearer to the earth than the sun, is the principal cause of tides. Because the force of gravity decreases with distance, the moon exerts a stronger gravitational pull on the side of the earth that is closer to it and a weaker pull on the side farther from it. The earth does not respond to this variation in strength because the planet is rigid—instead, it moves in response to the average of the moon’s gravitational attraction. The world’s oceans, however, are liquid and can flow in response to the variation in the moon’s pull. On the side of the earth facing the moon, the moon’s stronger pull makes water flow toward it, causing a dome of water to rise on the earth’s surface directly below the moon. On the side of the earth facing away from the moon, the moon’s pull on the oceans is weakest. The water’s inertia, or its tendency to keep traveling in the same direction, makes it want to fly off the earth instead of rotate with the planet. The moon’s weaker pull does no
