The Moon slows the Earth's rotation, but how fast was it spinning billions of years ago?
To calculate the exact speed of the Earth's rotation when the moon first formed is difficult and probably impossible because we don't have all the necessary data. However it is relatively easy to calculate an upper limit on the speed, because angular momentum of the Earth-moon system is more or less conserved. Current angular momentum of the system = angular momentum of the moon + angular momentum of the Earth angular momentum of the moon = Iw = mr^2 w + neglible contribution of moon's rotation mr^2 w = (7.3477x10^22)((3.84399x10^8)^2)(2pi/27.... = (7.3477x10^22)((3.84399x10^8)^2)(2pi/2.3... seconds) = 2.8899x10^34 Nms angular momentum of the Earth (approximation assuming uniform density) = (2/5)mr^2 w = (2/5)(5.97219x10^24)((6.3710x10^6)^2)(2p... = (2/5)(5.97219x10^24)((6.3710x10^6)^2)(2p... seconds) = 7.0514x10^33 Nms total angular momentum = 3.5950x10^34 Nms The speed of the Earth's rotation has been getting slower as the moon moves further away. That means if you press rewind, the speed of the Earth's rotation gets faster as the moon gets closer. The maximum speed of the Earth's rotation depends on how close the moon was when it was originally formed. We can assume, though, that the moon was no closer than in an orbit skimming the Earth. r = Rearth + Rmoon = 6.3710x10^6 + 1.73710x10^6 = 8.1081x10^6 m At this distance its angular speed w would be governed by GMearth/r^2 = (w^2)r w = sqrt(GMearth/r^3) = 8.6473x10^-4 which corresponds to an orbital period of about 2 hours. That's for the moon. Now we calculate the angular momentum of that orbit by the same formula as for the current moon. mr^2 w = (7.3477x10^22)((8.1081x10^6)^2)(8.6473x1... = 4.1771x10^33 Nms Deduct that from the total angular momentum to get the maximum angular momentum of the ancient Earth: 3.1773x10^34 Nms = (2/5)mr^2 w w = 3.2768x10^-4 rad/s which corresponds to a rotation period of about 5 hours. The number I've heard quoted was about 10 hours. That can be accounted for by the moon being somewhat higher than skimming the surface of the Earth (obviously it was), or the moon itself spinning very rapidly (probably it was spinning, but not that rapidly).
What would happen to the moon phases if the earth slowed down?
Nothing :) The Moon phases depend on the angle we could draw between the Sun and the Moon, from our point of view (called elongation). 180 degrees, by definition, mean an opposition, ie a full moon, no matter the rotation or shape or color or favorite song of Earth. The same applies for any other elongation :)However, the Moon is the one slowing down the Earth, so the Moon would probably be further out, making its orbital period longer. Longer full moons, yey. :P
If the Earth slowed down the Moon's rotation, why hasn’t the Sun slowed down the Earth's rotation?
It will, eventually. “Tidal locking” occurs because planets aren’t perfectly uniform masses - they have areas of greater and lesser density within them - and especially because of the “bulges” caused in each body by the tides (hence the name). The effect of the Sun’s gravity on these will gradually slow a planet’s rotation and eventually “lock” it so that only one face faces the parent body. But it is a very, very gradual process. The Moon has become tidally locked to the Earth because it’s relatively large and close. The Moon is also having an effect on the Earth’s rotation (actually, this effect is greater than that of the Sun, again due to the Moon’s size and relative closeness), but the Earth is not expected to become tidally locked to the Moon before the Sun becomes a red giant and engulfs both. Right now, the Earth’s rotation is slowing to the tune of about 15 microseconds more time per day, per year.
Why did the earth slow down the moon's rotation? How does it prevent the moon from spinning on its axis?
The Moon does spin. It's rate of rotation is more or less the same as its orbital period so it has one face we always see. The face we don't see is called the “far side” not the “dark side”. The “dark side,” or more properly the “night side” is the side opposite the Sun, which changes all of the time.This business of the Moon showing only one face to the earth is called “tidal locking”. The tidal force is the force that is the result of gravity being stronger on one side of a body than on the other.The Earth's tidal force on the Moon stretches the Moon into a football shape making a bulge on the near side and the far side. In the earlier history of the Solar system, the Moon was rotating faster than it is today. The tidal bulge was displaced by rotation, with its gravity pulling on the Earth, transferring angular momentum from the Moon to the Earth.Eventually the rotation of the Moon slowed to the point that it's tidal bulge was no longer displaced, and no longer tugging on the Earth in a way that would change the Moon’s rotation.Turnabout is fair play. The Moon exerts a tidal force on the Earth pulling the Earth into a football shape. The rotation of the Earth displaces the tidal bulge about 6°, tugging on the Moon.The effect is that angular momentum is transferred from the earth to the Moon, causing the Moon to accelerate in its orbit, causing the Moon to move farther out, and slowing the rotation rate of the earth.Eventually, the Earth will tidally lock wth the Moon. The Earth day will be about 40 current days long, as will the Moons orbit and day.
What happen to the earth if the moon is too far away? what happen if escapes the orbit?
The moon is spiraling away from Earth at a rate of 3.8 cm per year. Why? Earth's ocean tides are responsible. Within 500 million to one billion years, however, the Moon will have moved far enough from Earth that total eclipses of the Sun will no longer be possible for observers here on Earth. By this time, the Moon will have moved about 5% further from Earth than it is today and will be too small to completely cover the disk of the Sun. Any solar eclipse that occurs after this time will be only a partial eclipse. The tidal effect is not only causing the Moon to move further away from Earth but is also slowing the Earth down. While the tidal bulge leads the Moon and pulls it forward, the Moon also exerts a gravitational attraction on the tidal bulge that pulls it backward. As the ocean waters are pulled across the ocean floor, friction is created that slows the Earth's rate of rotation about its axis. This effect slows the Earth's rotation by 0.0018 seconds, or about two milliseconds, per century. This process began billions of years ago once the Earth and Moon had formed. The rate at which the Moon's orbit increased was faster then given the Moon's closer location to Earth. As the tidal effect caused the Moon to spiral outward, its own rotation rate was decreased until the Moon always showed the same face to Earth. The Moon was slowed much more rapidly given its much smaller size compared to Earth. It is estimated that the Moon's rotation stopped within about 50 million years of its formation. The Moon's gravitational pull causes the ocean to bulge towards it in high tide whenever the Moon is directly overhead. At the same time, the ocean on the opposite side of Earth also bulges, due to centrifugal and other forces. (Centrifugal force is what you feel when you're riding in a car that takes a corner very quickly.) As Earth spins, each ocean finds itself beneath the Moon about every 24 hours. Earth's gravity has caused the Moon to become tidally locked us as well as increasing the distance between the two worlds. By tidally locked, we mean that the moon's rotation rate is the same as the time it takes the moon to go once around Earth, which also results in us seeing only one side of the Moon.
Why is the Moon creeping away from Earth?
Conservation of angular momentum. The tidal forces that the moon causes on the Earth are gradually dissipating its orbital energy by friction and slowing its rotation (i.e. the day is getting longer). The total angular momentum of the Earth-Moon system has to be conserved. In order to compensate for the slowing of the Earth's rotation, the radius of the Moon's orbit has to increase.
Why is earth's rotation slowing down?
It’s not mysterious at all. Newton predicted it hundreds of years before it could be directly measured. Basically, the Earth is slowing down because the Earth spins “beneath” the Moon faster than the Moon revolves around it.The Moon’s gravity creates a tidal bulge on the Earth. This bulge attempts to rotate at the same speed as the rest of the planet. As it moves “ahead” of the Moon, the Moon attempts to pull it back. This slows the Earth’s rotation down.One of the rules of the Universe is that “angular momentum” can’t go anywhere — even if individual pieces speed up, slow down, or change direction, the sum total of angular momentum cannot change. The Earth loses angular momentum when the Moon slows it down, so the Moon has to gain it — and it does, by moving further away in its orbit. The Moon is currently receding from the Earth by about one and a half inches per year.Exactly the opposite thing is happening to Mars’ innermost moon, Phobos. Phobos revolves around Mars faster than Mars rotates, so Phobos is speeding up Mars’ rotation — and is also slowly spiraling inward as a consequence. As a result, Phobos will crash into Mars in about fifty million years.ETA: Chris Dybala pointed out through suggested edits that I had gotten the recession rate of the Moon wrong — it’s about one and a half inches per year, not one and a half centimeters. He also suggested changing the amount of time it would take Phobos to crash into Mars to fifty million years, which seems to fit the range I see most often (thirty to fifty), but I’ve seen papers that predict it in as few as ten; there seems to be substantial ambiguity in measuring tides on Mars’ complex crust resulting from such a very tiny rock.
Why exactly is the moon tidally locked to the earth?
This is actually the case for nearly all moons of the solar system of any significant size. The reason for tidal locking is that gravity is significantly non-uniform across the target body (moon). The nearest part of the moon (not necessarily Earth's moon) is closer to its host planet than the farther side of the moon, and thus the nearest part of the moon experiences a greater gravitational force per unit mass. As the moon responds to the associated gravitational fields, the near side leads and the far side lags, and the entire moon stretches out as a whole. This distorts the shape of the moon along the line from planet to moon. If enabled to swing like a pendulum, which it initially will be, a distorted moon will have its equilibrium position when the stretching line is in line with the line to the planet. Torque from the gravitational forces on this warped moon will restore it to this equilibrium position. This is where the moon will settle once the initial rotational energy dissipates internally as tidal heating. Anytime the moon swings out of this equilibrium position, a new set of tidal stresses squish and squash it, converting the rotational energy into thermal energy. The ultimate ending is that the bodies become tidally locked to one another. Usually, the satellite body tidally locks LONG BEFORE the host body does. The sun is so far away that its gravitational forces are so uniform that the tidal influence is insignificant on the moon's motion. Earth's tidal influence is a lot more important.
If you shout on moon,will sound travels faster or slower on earth ?why?
On the moon , there is total vacuum = there is no "matter " ==> there is nothing that the sound could use to travel (sound needs matter to travel) , so , you're shout won't be heard!