tidal forces and gravity?

Question

i was reading about tidal forces and gravity, and although they are interlinked with one another, i don t really understand their differences....can someone help me with that? explain to me the differences between tidal forces and gravity? thanks

Answer 1

The main point is that tidal bulges occur because the water nearest the moon experiences more gravitational acceleration than the center of the earth does, and the water on the far side experiences less. This change of acceleration with distance is called the gravity gradient (which you can google for more information.). Both differences have the effect of accelerating the water away from the center of the earth. And of course it's the rotation rate of the earth relative to the moon's orbit around the earth that determines lunar tidal frequencies.
One effect of tides, on earth and other planets, is that friction (on earth, between the ocean and its floor) drags the bulges beyond the nearest and furthest points. This results in energy and angular momentum loss for the earth; its rotation rate is constantly slowing. How is angular momentum conserved? The asymmetrical bulges actually result in a slightly "forward" gravitational force on the moon, which adds energy and angular momentum to its orbit. The total angular momentum stays the same although energy is lost in the frictional ocean drag.

Answer 2

Water, a liquid, is a mass m, just like any solid or gas is also mass. And gravity attracts mass no matter what kind of mass it is. We see this in the equation F = GmM/R^2; where G is a constant, m and M are masses (like the moon M and oceans m), and R is the distance between the two masses.

F is the attraction force between the oceans and our Moon in this example. So the Moon actually pulls on our oceans. When that happens the ocean bulges outward toward the Moon and that's what we call high tide. Where the Moon is not pulling on the water, the ocean recedes at bit. That's what we call low tide.

As the Moon swings around Earth, the bulge in the oceans follows it. Thus, at one moment the tide will be high, but later, as the Moon moves on, it will recede to be a low tide. As you might imagine, the forces of such enormous bodies of water rising and falling periodically are extremely high. These are the tidal forces.

Interestingly, the Sun also pulls on our oceans. So, in reality, the tides are caused not only by the Moon, but also by the attraction forces from the Sun. And, of course, the Sun does not rotate around the Earth, but the Earth's rotation makes it seem like it does. When both the Moon and the Sun are acting on the same parts of the ocean, we get really high tides because of that extra gravitational force.