Driving on the moon

Originally posted by uzless
Ok, how bout if you immediately threw the gear shifter into reverse after you lift off. The tires would be rotating backwards, thus propelling the car forward if i understand your point.

Would this not provide you with additional forward momentum?

All that would do is tend to cause the car to tumble at the most. There would be no contribution to acceleration. How 'bout this: as the wheels leave the ground, there are spikes that can stick out from the center of the tires. So you just get off the ground, these spikes stick out and you are again contacting the ground and getting more forward momentum. Enough to stay off the ground?

Originally posted by sonhouse
Its a thousand years from now, there is a freeway round the moons' equator and it has been surveyed and evened out so it's perfectly circular within a mm. So this electric car with a normal drive like an electric car of today, but the wheels can turn 50,000 RPM if they have to or more, they are a meter in diameter and can take the spinning forces involved w ...[text shortened]... question is, can you drive it into some sort of orbit, even if its only a cm above the ground?

No.

Originally posted by GinoJ
No.

Prove it.

Originally posted by sonhouse
All that would do is tend to cause the car to tumble at the most. There would be no contribution to acceleration. How 'bout this: as the wheels leave the ground, there are spikes that can stick out from the center of the tires. So you just get off the ground, these spikes stick out and you are again contacting the ground and getting more forward momentum. Enough to stay off the ground?

would depend on the length of spikes but in theory, if the spikes were long enough and the car was an open wheel car, (ie no wheel well for the spikes to hit), then it would be possible i'd say.

The spikes would have to gradually get longer as the car got higher off the ground.

Originally posted by uzless
would depend on the length of spikes but in theory, if the spikes were long enough and the car was an open wheel car, (ie no wheel well for the spikes to hit), then it would be possible i'd say

I was thinking that since you are already in some low-lying sub-orbital path if you had spikes, they could give you some more thrust when you are off the ground just for a small amount of time, maybe enough to make a differance in whether you would be fully in orbit or not. PEB6, any way to calculate the differance?

Originally posted by sonhouse
I was thinking that since you are already in some low-lying sub-orbital path if you had spikes, they could give you some more thrust when you are off the ground just for a small amount of time, maybe enough to make a differance in whether you would be fully in orbit or not. PEB6, any way to calculate the differance?

The spikes might work, because as the car begins to lift off the ground the spikes would still be able to push off the sides of the spike wells and provide thrust. Not sure how to calculate this, though.

I had another idea too...chemical attraction between the tire and the moon track. This is not as far fetched as it sounds, snow tires actually work this way. The rubber used for snow tires is stickier in cold weather, but wears down much faster in warm weather; the tread patterns do almost nothing for the grip. With chemical attraction, the equation changes from:

f(gravity) = f(centripetal acceleration)

to:

f(gravity) = f(centripetal acceleration) + f(chemical attraction)

Now if the centripetal acceleration balances gravity, there is still some traction due to the chemical attraction, and therefore room to increase the speed to orbital velocity.

Originally posted by PBE6
The spikes might work, because as the car begins to lift off the ground the spikes would still be able to push off the sides of the spike wells and provide thrust. Not sure how to calculate this, though.

I had another idea too...chemical attraction between the tire and the moon track. This is not as far fetched as it sounds, snow tires actually work this w ...[text shortened]... on due to the chemical attraction, and therefore room to increase the speed to orbital velocity.

Isn't that basically what happen's to drag race tires? Maybe not chemical but you can visualize what is going on, the track has small rocks in it and the rubber of the tire gets sort of built up in the area of the rocks and sticks making the contact to the ground more akin to a couple of gears than just a rubber contacting with viscous forces.
I think that's the only way to explain the fact those dragsters are getting WAY more than one G of accel. 1 G of accel over a 1320 foot track (1/4 mile) average, would only get you to about 175 miles per hour or 280 Km/hr. They are actually getting close to 300 MPH. The only explaination is my gear and tooth model. So the same thing could happen on the moon with two caveats: If the vehicle has the same mass as a dragster, say some 1500 pounds or 730 Kg, the actual weight on the moon would be 1/6th of that or about 120 Kg, 260 pounds, which would mean that much less force for traction. However, if you can triple the accel on earth you should be able to triple the accel on the moon over what you would expect if there was just regular traction, which would limit you to about 1.6 M/s/s as opposed to 9.8 on earth. However, triple that 1.6 and you get 4.9 M/s or about half a g of actual accel. So 1678 M/s required would take a little over 5 minutes if the tires held up that long. But the wieght would get less and less as time goes on so that 3 lunar g's would have to get less and less also, reaching zero when the tires no longer contacted the road. But my spikes could kick in at that point to give a bit more. It sounds like the average accel would be not 0.5 G's but about 0.25 G's, which would mean more like ten minutes to reach orbital velocity. Ah, Just thought of something else: Magnets. Suppose the road had a significant iron content and the car had a powerful electromagnet holding it down. Then the tires would be able to accel the beast as long as it wants and it would stay on the ground. The force would only need to be = to the lunar wieght of the vehicle, we said what, 120 odd Kg? Then when you reach the required velocity, you turn off the magnet and boing, you are in orbit. Or leave the magnet on, go even faster and you drive right off the frigging moon!

In an elliptical or circular orbit the same orbit is repeated on each revolution. Now, at the instant the car enters orbit it is touching the ground. When the car comes back to that part of the orbit it will graze the ground at that point. Thus it cannot enter an orbit that is above the ground at all points.

Edit: On reflection this assumes that nothing about the car changes while it is off the ground and that it stays at the same angle relative to the ground while off the ground. If, for example, the wheels shrunk while the car was in orbit the car's center of mass would return to the same spot but the wheels would now not touch the ground.

Originally posted by GregM
In an elliptical or circular orbit the same orbit is repeated on each revolution. Now, at the instant the car enters orbit it is touching the ground. When the car comes back to that part of the orbit it will graze the ground at that point. Thus it cannot enter an orbit that is above the ground at all points.

Did you read my last thread? I upgraded the car. You can do that in thought experiments! My newly upgraded car has an electromagnet pulling it down to the newly ironized roadway so it can achieve greater than orbital velocity so it can drive as fast as it wants now, the exit velocity would be modulated by the timing of when you turn off the electromagnet. It would in effect give you artificial gravity, at least as far as the tires are concerned. See how we demolished all that other ancient thought experiment!. Interesting thing is, such a device would actually work. In reality, it would be an electromagnet that would have hall sensors that would cause it to hover and then use a system like the linear motor, now tires are not needed. At first the lifting force would be the same as the weight, say 120 Km if our car is comes in at 727 Kg on earth so it starts off floating then magnetically accelerates
also and the lifting force would have to be balanced with a pulling force eventually because the car would be approaching weightlessness and if not for the magnet field would try to establish an orbit. But the magnetic field downward force would increase to keep the vehicle at the same distance off the ground. At some point, you could achieve orbit or keep on and reach escape velocity, or even higher, and drive, say, to Mars! Now we have a space transport system for real. It would be similar to an electromagnetic rail gun.
Another point of such a system, our freeway runs all the way 'round the moon and has been leveled out so it has a perfectly circular path around the equator of the moon. Such a system would allow you to have starting and exiting points anywhere around the giant circular path so you could start at point A, accel to point B with velocity C which you have precalulated to put you on a course for mars or Venus or Pluto for that matter. You would not be limited to one lunar G of accel, you could accel at say 10 G's or 100 G's if no people were inside. 100 EARTH G's, 9800 M/s/s. At that rate, you can get to 160 Km/s in 16 seconds! You can slingshot in a straight line anywhere in the solar system. Of course you would have to have the means to lose the delta V if you want to actually visit someplace but thats another story.

I have thought that it impossible to get into an orbital velocity with the only contact to the road with the wheels.
Now I have the solution of how it is done:

You can never get a velocity high enough to lift from ground. I've stated it before and I don't doubt that I'm wrong in this. But when you have reached this velocity, why not just pull up the wheels? Then you already have orbital velocity, a few cm above the read, and thus in orbit, you don't fall back.

I think this is the solution of the problem.

Originally posted by uzless
Ok, how bout if you immediately threw the gear shifter into reverse after you lift off. The tires would be rotating backwards, thus propelling the car forward if i understand your point.

Would this not provide you with additional forward momentum?

No; there would be angular acceleration about the center of mass of the car, but not forward acceleration.

Originally posted by FabianFnas
I have thought that it impossible to get into an orbital velocity with the only contact to the road with the wheels.
Now I have the solution of how it is done:

You can never get a velocity high enough to lift from ground. I've stated it before and I don't doubt that I'm wrong in this. But when you have reached this velocity, why not just pull up the w ...[text shortened]... ead, and thus in orbit, you don't fall back.

I think this is the solution of the problem.

What do you think about the addition of a controllable magnetic field holding you down till you reach whatever velocity you want? Would't that work? Did you read that thread?

Originally posted by sonhouse
What do you think about the addition of a controllable magnetic field holding you down till you reach whatever velocity you want? Would't that work? Did you read that thread?

You mean that the road is build of iron and you have electromagnets attached by the car? Then there will be no velocity limits.

In an ordinary amusement park roller coaster you have a special rail and you hold the cars in place with wheels on either sides so up-side-down manoeuvres and negative G are possible. Perhaps this is also a solution.

But when you let go of the road you will enter a elliptic orbit where half of the orbit is over the lunar surface and the other half is under. So you need, anyway, another push of some kind to the vehicle to convert the orbit to a kind where all of the orbit is over the surface.

Originally posted by FabianFnas
You mean that the road is build of iron and you have electromagnets attached by the car? Then there will be no velocity limits.

In an ordinary amusement park roller coaster you have a special rail and you hold the cars in place with wheels on either sides so up-side-down manoeuvres and negative G are possible. Perhaps this is also a solution.

But wh ...[text shortened]... e kind to the vehicle to convert the orbit to a kind where all of the orbit is over the surface.

Yes and if the electromagnet can act as a linear electric motor, google them if you don't know about them, then it can both levitate and acellerate to any velocity, no wheels touching the ground. If you truly have a circular roadway with iron in it all the way round the moon by carefully managing your acelleration, final velocity and aiming points, you can sling yourself right off the planet at interplanetary velocities to go to any destination in the solar system. Get the picture here?