Celestial Pull: Understanding Tidal Forces

If gravity is a pull between objects, then the Moon and Sun pull on the Earth's water. If this pull causes the water to move toward them, then the ocean levels will rise and fall as the Earth rotates.

If the Moon is closer to one side of the Earth, then its gravity pulls stronger on that side. If this uneven pull stretches the water into a bulge, then we call that effect tidal forces.

If the strength of gravity depends heavily on distance, then a closer object will have a bigger impact. If the Moon is thousands of times closer than the Sun, then it will be the main driver of our tides.

If the Sun and Moon pull in the same direction at the same time, then their gravity adds together. If their combined pull is extra strong, then the resulting high tides are called spring tides.

If a spring tide requires the Sun, Earth, and Moon to be in a straight line, then it must happen when the Moon is either between the Earth and Sun or on the opposite side. If these positions match the New and Full Moon, then those are the phases when they occur.

If gravity pulls on all matter, then it pulls on both the water and the land. If the water is liquid and moves more easily than solid rock, then we only see the "bulge" clearly in the oceans even though tidal forces act on the whole planet.

If the Sun pulls in one direction and the Moon pulls in another, then they cancel out some of each other's strength. If the total pull is weaker, then the difference between high and low tide is smaller, which is a neap tide.

If distance reduces the power of gravity more than size increases it, then the distant Sun will have a smaller effect. If the Sun's pull is less effective at stretching the water, then it creates weaker tidal forces.

If the Earth has two tidal bulges (one on the side facing the Moon and one on the opposite side), and if the Earth rotates once a day, then a single spot on the beach will pass through both bulges. If it passes through both, then it sees two high tides.

If the Moon pulls the water toward it, then a bulge forms on the near side. If the Moon also pulls the Earth away from the water on the far side, then a second bulge is left behind on the opposite end.

If the Moon is at a right angle to the Sun during the quarter phases, then their gravitational pulls do not work together. If they work against each other, then we experience the weaker neap tide.

If the water bulges stay lined up with the Moon while the Earth spins underneath them, then the land moves into and out of the high water. If this movement creates the daily tide cycle, then it is caused by tidal forces.

If tidal forces require a huge area of water to "stretch" and move, then a small body of water cannot show the effect. If a pond is too small to have a significant difference in the Moon's pull from one side to the other, then no visible tide occurs.

If the water is being pulled into bulges in other parts of the world, then it must be pulled away from your current location. If the water level drops because it is moving toward a bulge elsewhere, then you are at low tide.

If the Sun and Moon are competing rather than helping each other, then the water doesn't move as much. If the tide range is at its minimum, then it is a neap tide.

If the Sun is very far away, its stretching power is reduced. If measurements show it has about 46 percent of the Moon's power, then the Sun provides roughly half of the total tidal forces we feel.

If gravity pulls on everything with mass, then it must pull on the air and the ground. If the air is thin and the ground is hard, the movement is small, but tidal forces still cause them to bulge slightly.

If gravity is stronger when objects are closer together, then the Moon's pull increases at perigee. If the pull is stronger, then the resulting tidal forces create larger bulges and higher tides.

If you measure the water at its highest point and then at its lowest point, then the gap between those two numbers is the range. If the range changes based on the Moon's phase, then it describes the strength of the tides.

If the Moon is orbiting the Earth while the Earth is spinning, then the Earth has to rotate a little extra to "catch up" to the Moon's new position. If this takes about 50 extra minutes, then the tidal forces cycle is actually 24 hours and 50 minutes long.