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To Everywhere in 42 Minutes

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Re: To Everywhere in 42 Minutes

#41

Post by lisper »

ars wrote: post #38
lisper wrote: post #36

Earlier quoted context omitted.

That's why I qualified with "most" and "virtually." I haven't actually done the math, but I'd be surprised if it didn't work out to something like >90% of the total energy for a long trip going into frictional losses. Consider any vehicle: the amount of the total energy that goes into generating actual motion is roughly proportional to the time it takes to accelerate to your final cruising speed, at which point all o…

For a car you are 100% right - it's nearly all friction. But to accelerate to over 1000 MPH you need a lot of energy just to get started, and you have little chance of recovering it. But an overland bullet train in a vacuum would be so much easier to build that the acceleration energy would be worth it.

> But to accelerate to over 1000 MPH you need a lot of energy

You need exactly 4 times as much energy as you do accelerate to 500 MPH, which is the speed of a slow jet. Four times a small amount is still a pretty small amount.

Re: To Everywhere in 42 Minutes

#42

Post by david927 »

david927 wrote: post #18

Silly. It took us 24 years to get 12km straight down, and that's the best we've ever done. http://www.damninteresting.com/?p=567

Actually, screw traveling -- if we could just drill a few hundred meters easily and cheaply, we could solve all our energy problems.

Temperatures roughly increase about 1 degree C for every hundred meters you go down. The difference could power a Stirling Engine (some of which are powered on differences of as little as .5 degrees C). It seems to me you could use a captive bolt pistol to get down just a few hundred meters, carrying a plastic tube which would have two chambers. The engine would pump the water and generate additional electricity. What do you guys think?

Re: To Everywhere in 42 Minutes

#43

Post by lisper »

lisper wrote: post #41
ars wrote: post #38

Earlier quoted context omitted.

For a car you are 100% right - it's nearly all friction. But to accelerate to over 1000 MPH you need a lot of energy just to get started, and you have little chance of recovering it. But an overland bullet train in a vacuum would be so much easier to build that the acceleration energy would be worth it.

> But to accelerate to over 1000 MPH you need a lot of energy You need exactly 4 times as much energy as you do accelerate to 500 MPH, which is the speed of a slow jet. Four times a small amount is still a pretty small amount.

BTW, the math in this case is really easy. Kinetic energy is 1/2mv^2. 1000 MPH is 444m/s. So to accelerate a one metric ton vehicle to 1000 MPH requires 1/21000 444^2 = ~100MJ, which is less than the energy in one gallon of gasoline.

Re: To Everywhere in 42 Minutes

#44

Post by ars »

lisper wrote: post #43
lisper wrote: post #41

Earlier quoted context omitted.

> But to accelerate to over 1000 MPH you need a lot of energy You need exactly 4 times as much energy as you do accelerate to 500 MPH, which is the speed of a slow jet. Four times a small amount is still a pretty small amount.

BTW, the math in this case is really easy. Kinetic energy is 1/2 m v^2. 1000 MPH is 444m/s. So to accelerate a one metric ton vehicle to 1000 MPH requires 1/2 1000 444^2 = ~100MJ, which is less than the energy in one gallon of gasoline.

Any vehicle would probably by much heavier than 1 ton. A 747 weighs about 400 metric tons. But still 400 gallons of gas (in bulk) only costs about $750 which is nothing.

Although that assumes you got perfect efficiency from it, which you won't.

I concede your point - and you should have gotten more mod points for it.

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