3 ms·

>at the time Your numbers need adjusted for 30 years of fuel efficiency improvement (but to be honest I think your calculations would still illustrate the same

by ac2u 6y ago

>at the time Your numbers need adjusted for 30 years of fuel efficiency improvement (but to be honest I think your calculations would still illustrate the same point). The passage I'm reading doesn't cite an exact study/paper except to cite that it's from the works of Dmitri Orlov. I think the point was more likely centred upon 1:1 calorie transport/consumption of the variety of staples needed rather than taking one of the most calorie dense categories of food like meat for the purpose of back of the envelope math. I also took a quick glance at a passage from Google from Orlov's book which takes all the calories involved in the growth of the food as well, so there's probably a little more to it.

credit_guy 6y ago
Most people don't realize how huge chemical energy is compared to mechanical energy. Here's a different way to look at the same thing: one gram of carbs has an energy content of 4.2 kcal. That's about 18000 Joules. One Joule is the same as 1 kg*m2/s2; it takes one Joule to lift a mass of 1kg to a height of about 10cm (because the gravitational acceleration is about 10m/s2). So, with 1 Joule you can lift one gram to a height of about 100 meters. With the energy content of 1 gram of carbs, you can lift 1 gram of matter to a height of 1800 kilometers, i.e. more than 4 times higher than the orbit of the International Space Station. When shipping things around, we don't change the elevation too much, for the simple reason that the highest elevation on Earth is less than 10km. Moving 1g of matter 1km in the horizontal direction requires much, much less energy that 1km on the vertical. Now food has some water content, the energy does not get converted with 100% efficiency, etc. But the idea that the energy used in transportation is anything close to the energy content of food is quite far fetched. Let's put it differently: it's hard to lose weight. It's damn hard. Precisely because the energy content stored as chemical energy in our fat cells is so large compared to how much we burn by performing mechanical actions. For example, an average runner burns about 100 (kilo)calories per mile. Since one pound of fat has about 3500 kcal, you need to run about 35 miles to burn that. If you want to burn all the energy stored in all your body, you need to run more thousands of miles. And we humans, are very inefficient. We don't have wheels in particular. Or, let's put it yet another way. One of the most inefficient ways to transport things around is by rocket. The planned Starship will have a launch mass of about 5000 tons and a payload of 100 tons in orbit. That's a ratio of 50:1. So, to take one gram of stuff from being stationary on Earth to moving at orbital speed (8km/s) perpetually in the sky it takes about 50g of propellant (fuel plus oxidizer). When we move things on Earth, we obviously can use the Oxygen that's all around us. Of the 50g of propellant, only about 11g are actual fuel, so you end up with a ratio of about 11:1 of fuel vs payload, using the most inefficient way of moving things around.
- aidenn0 6y ago
  On top of that we can't eat hydrocarbons, but we can use them to move food around.

by ac2u 6y ago

credit_guy 6y ago

Most people don't realize how huge chemical energy is compared to mechanical energy. Here's a different way to look at the same thing: one gram of carbs has an energy content of 4.2 kcal. That's about 18000 Joules. One Joule is the same as 1 kg*m2/s2; it takes one Joule to lift a mass of 1kg to a height of about 10cm (because the gravitational acceleration is about 10m/s2). So, with 1 Joule you can lift one gram to a height of about 100 meters. With the energy content of 1 gram of carbs, you can lift 1 gram of matter to a height of 1800 kilometers, i.e. more than 4 times higher than the orbit of the International Space Station. When shipping things around, we don't change the elevation too much, for the simple reason that the highest elevation on Earth is less than 10km. Moving 1g of matter 1km in the horizontal direction requires much, much less energy that 1km on the vertical. Now food has some water content, the energy does not get converted with 100% efficiency, etc. But the idea that the energy used in transportation is anything close to the energy content of food is quite far fetched. Let's put it differently: it's hard to lose weight. It's damn hard. Precisely because the energy content stored as chemical energy in our fat cells is so large compared to how much we burn by performing mechanical actions. For example, an average runner burns about 100 (kilo)calories per mile. Since one pound of fat has about 3500 kcal, you need to run about 35 miles to burn that. If you want to burn all the energy stored in all your body, you need to run more thousands of miles. And we humans, are very inefficient. We don't have wheels in particular. Or, let's put it yet another way. One of the most inefficient ways to transport things around is by rocket. The planned Starship will have a launch mass of about 5000 tons and a payload of 100 tons in orbit. That's a ratio of 50:1. So, to take one gram of stuff from being stationary on Earth to moving at orbital speed (8km/s) perpetually in the sky it takes about 50g of propellant (fuel plus oxidizer). When we move things on Earth, we obviously can use the Oxygen that's all around us. Of the 50g of propellant, only about 11g are actual fuel, so you end up with a ratio of about 11:1 of fuel vs payload, using the most inefficient way of moving things around.

aidenn0 6y ago
On top of that we can't eat hydrocarbons, but we can use them to move food around.