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Say...One had a planet slightly smaller than Earth, with a thick atmosphere, but it had a rotational period of about 243 days.How would one increase the rate of spin (decrease the length of day) down to about a 24 hour day?One option might be to attach some huge jet engines or rocket engines to the surface, and let them blast away at the atmosphere. Would this have any net effect as the wind would spin a bit, but would eventually stop. So, logically it might not have a permanent effect on the planetary rotational speed once the engines were stopped.Perhaps selectively bombard the planet with eastward, or westward (depending on preference) asteroids and comets. But, that might be like trying to move a truck with a BB gun. One would need a lot of BBs.Other ideas?
Clifford, your first example is not correct because your jet engines would produce an opposite force on the ground (action=reaction). The best way would probably be to fire cannon balls at low angles and at a higher speed than escape velocity.
The best way would probably be to fire cannon balls at low angles and at a higher speed than escape velocity.
Could a large, low-orbit object do much? Sort of like the opposite to a gravitational slingshot?
CliffordK, are you some sort of inter-planetary adventurer that requires this information to save your homeworld? It seems like a very specific problem you have posed.
has anyone ever seen CliffordK and Superman in the same room together?
It would be a monumental task to cool the core of a planet, and may not produce the desired output, as a spinning planetary core may help produce a magnetic field that would protect the planet form solar wind and cosmic rays.There are theories that much of the motion of the planets is due to the spinning of matter in the protoplanetary disk around the early sun. The two innermost planets (Mercury and Venus) have the slowest rotation so it seems unlikely that the rotation of the sun is powering the rotation of the planets. Also consider our moon is tidally locked with the Earth, rather than being spun by the Earth.As far as just pushing on the atmosphere, the reason I don't think it would work is this.Consider lobbing cannon balls the length of a football field. When you fire them off, they would impart a slight acceleration to the planet. However, when they land, they would impart a negative acceleration to the planet, and the net would be zero acceleration.I think I wrote this earlier in a similar topic. Consider if you were in a closed school bus with perfect bearings. And you had a pile of shot-puts at the front of the bus, so you would pick up the shots and throw them at the back of the bus. The bus might lurch forward slightly when you throw the shot-put, but then it would stop again when it slammed into the back of the bus. And, in fact, carrying the shot-puts back to the front of the bus to try again might erase all progress that was made. Likewise, a fan inside the bus with all the windows closed would be ineffective in moving it.So, blowing in the atmosphere, or using a propeller in an ocean would be ineffective if the planet slowed or dissipated the movement.Quote from: CPT ArkAngel on 28/08/2012 00:10:27The best way would probably be to fire cannon balls at low angles and at a higher speed than escape velocity.One would have to contend with the atmosphere when firing the cannon balls, unless perhaps one would first condense the atmosphere, then fire the cannon balls in a thin atmosphere. If you could fire the cannon balls around the sun, then allowed them to impact the planet on the opposite side, one might be able to conserve mass and maximize the energy gain. Although, perhaps the overall quantity of matter needed to start the planet, or the planet's crust spinning would be relatively minimal.Quote from: bizerl on 27/08/2012 23:38:04Could a large, low-orbit object do much? Sort of like the opposite to a gravitational slingshot?Using tidal forces alone to start a planet spinning would be an excruciatingly slow process, and might take billions of years. Rather than slingshotting around the sun, one might be able to fire a rocket, slingshot around the moon, and impact the planet in the opposite direction, slowly converting rotational momentum of the planet to orbital velocity of the moon.Too small of a moon, and one would send the moon speeding too fast. Of course, if the planet did not have a moon, one would have to be captured.
With effects like several of those discussed in this thread -- firing of cannon, cycling of water at different elevations, etc. -- it is possible to alter a planet's angular orientation, but not its angular momentum. Angular momentum of a system must be conserved. So must energy. The angular velocity of the Earth is gradually decreasing all the time (length of day increasing) because of tidal friction (moon and sun) causing heating. The angular momentum is conserved by the moon moving slowly further away from the Earth, and the Earth's orbit moving slowly away from the sun.It is quite easy to work out the angular momentum of a planet, and the amount of angular kinetic energy that would be needed to reduce it to near zero. That would be a useful thing to do for the Earth, because the Earth and Venus are near-twin planets in terms of size and density (the most recent measurements suggest that Venus is almost exactly the same size as the Earth, but about 10% less dense. So if we calculate the angular kinetic energy of the Earth's rotation, then that will be about 10% larger than the amount of kinetic energy it would take -- applied kinetically as a tangential couple -- to speed up Venus' rotation to a similar rate to the Earth's.The Earth's kinetic energy of rotation is, according to this website -- qntm.org/data -- 2.5786 E29 J World annual energy consumption is, according to wikipedia -- en.wikipedia.org/wiki/World_energy_consumption -- 4.74 E20 JThis means that the energy that would have to be invested to speed up the rotation of Venus, if it could be applied efficiently, would correspond to 400 million years of the world's current total energy consumption. And unfortunately, the two conservation laws -- angular momentum and total energy -- are set in stone.
With a small magnetic field over the earth you can spin it up or slow it down.
From William:Quote Neither the great Benjamin Franklin nor the great Nikola Tesla ever achieved this. There has been no change in the earth's rotation other than a steady increase in day length of the order of 2 milliseconds per century. There has been no report of any human tampering affecting the length of day (other than the prayers of Joshua and King Hezekiah). Over the last two centuries the Royal Greenwich Observatory (among other institutions) has been carefully monitoring the length of sidereal day (solar day does vary in a regular seasonal fashion), and observed no departure from the regular pattern in spite of significant variation in the Earth's magnetic field, and in external magnetic fields affecting the Earth.Variations in the Earth's magnetic field have been observed in the wandering of the magnetic poles and in quite significant changes in field strength. Variations in external magnetic fields occur with swarms of charged particles from solar storms passing the Earth.That is because they were not lunatics, and cowards like many of the "modern scientists", just itching to push the button on something new and unknown to them. Which is just about everything around them. The earth is propelled by external forces, it is created and kept in creation by external forces. As you make metal thinner or smaller in diameter. It starts to lose some of its tenacity. Look at the edge of very thin metal under a microscope, it is no longer, that smooth hard metal surface, it is more like a ceramic or glass. Very brittle and uneven. That would not be the case if, as "modern scientists" claim that the strength of attraction was from the inside. In fact everything is under pressure, from ambient radiation from outside the object. So as things get smaller, there is less time for ambient radiation entering on the far side of the object to positively accelerate, which would leave a vacuum, or shortage of particles of electricity in the object. As soon as the ambient radiation enters the thin objectat reduced speed, it is suddenly leaving to a place that is equally abundant with particles of electricity. Causing a certain amount of repulsion, because of a bottle neck or buildup of partices of electricity. If we take a low velocity 45 caliber round, we can blow a hole in a 1/16" plate with ease. It makes a perfect hole and you can reclaim the round, it is still in good condition. If though we take the same round at the same velocity and fire it at a 3/16" plate of the same material, the round smashes and turns to dust, on the surface. It will not even remove the paint that is on the surface of the 3/16" metal. Where on the 1/16" plate it goes right through. It is all about the surface of the metal being able to create a counter force, of electromotive force. The thin plate was unable to create the conductance necessary to maintain a shortage of particles of electricity in the plate. Once there was an abundance of particles of electricity in the metal itself, the material is as easy to penetrate as liquid. The thicker material is able to create an ARC ray powerful enough to destroy the round. Basically turn the round into a liquid that does not have enough capacitance to destroy the metal it is striking. If any of you saw the 9/11 video of the plane striking one of the towers, you may have seen the ARC ray in front of the plane, and a smaller ARC ray, coming off the building. The plane won and cut right through steel "H" beams. Even though it was aluminum, at reduced speeds it could never happen. It is just an electrical effect. Much like a plasma cutter. We know that at a stand still, it requires hundreds or thousands of times more energy, to put holes in objects, that bullets put holes in with ease, and with very little actual force. It is just an electrical effect. There is almost no force from a bullet. When you see guys with bullet proof vests, flying around, that is the movies. You might not even know you were hit by a rifle round if you were wearing the correct body armor. The bullet is basically a plasma cutter. Since a plasma cutter cuts through just about anything it is pretty effective. The lunar module used a special magnetic field, to connect high velocity objects like meteorites, electrically, with the Lunar module to take away any advantage of the moving object. This was all well known and has been taken away from the public for the most part. Sincerely, William McCormick
Neither the great Benjamin Franklin nor the great Nikola Tesla ever achieved this. There has been no change in the earth's rotation other than a steady increase in day length of the order of 2 milliseconds per century. There has been no report of any human tampering affecting the length of day (other than the prayers of Joshua and King Hezekiah). Over the last two centuries the Royal Greenwich Observatory (among other institutions) has been carefully monitoring the length of sidereal day (solar day does vary in a regular seasonal fashion), and observed no departure from the regular pattern in spite of significant variation in the Earth's magnetic field, and in external magnetic fields affecting the Earth.Variations in the Earth's magnetic field have been observed in the wandering of the magnetic poles and in quite significant changes in field strength. Variations in external magnetic fields occur with swarms of charged particles from solar storms passing the Earth.
Another option might be to move a asteroid such as Ceres into an elliptical planet crossing orbit, and force it to crash into Venus at the appropriate place and angle. Of course, the risk is that if a large asteroid from beyond Earth is moved into a Venus crossing orbit, it would also be in an Earth crossing orbit.Could I gain enough energy by merely changing the eccentricity of one or more asteroid orbits?No doubt some of the physicists here will tell me that it is too much energy alter the eccentricity of orbit of a large asteroid or dwarf planet into a Venus crossing orbit. Or, that a tangential impact of Ceres would not be enough to make a 24 hour day.And, of course, we would have to be far more advanced than we are today to convince any government to allow one to move an potentially planet killing asteroid into an Earth crossing orbit, especially if it would be a multi-generational project.
Clifford, I am afraid that your very nice orbital diagrams are in error. The sun is at one focus of any elliptical orbit, not at the geometric centre.