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I am not a mechanical engineer, but my general understanding is even mammals cannot be scaled up arbitrarily. I've read that elephants are more or less the maxi

I am not a mechanical engineer, but my general understanding is even mammals cannot be scaled up arbitrarily. I've read that elephants are more or less the maximal size of land-based mammals because of heat transport. The surface is not large enough to transport all the heat away from the body. I could imagine that similar effects limit mechanical designs.

emteycz 5y ago
The height of trees is limited by the physical limits of water transport.
pyuser583 5y ago
“The surface is not large enough to transport all the heat away from the body” Can you explain that a bit more? I don’t understand.
- cmyr 5y ago
  As a body increases in size, the surface area increases as a square but volume increases as a cube. The more volume, the more heat, and after a certain point your available surface area is no longer adequate to vent that heat. Another example of a similar principle applies to insects: they don’t have lungs, and absorb oxygen directly through their skin. In earlier eras of earth’s history, there was much more oxygen in the air, and so insects could be much larger, because the same amount of surface area could absorb enough oxygen to fuel a larger number of cells.
- ncmncm 5y ago
  Look up "square-cube law". It governs everything about animal size. But not vehicles, so much. The principle is that 2x size, i.e. 2x length, 2x width, 2x height, gives you 8x volume and, for animals, mass. All that mass has to be kept fed and aerated, and produces heat. But the surface area didn't go up by 8x. It only went up 4x unless you changed the shape a lot. You probably can't get skin to shed heat 2x as well, so you have to be careful not to produce 8x as much heat, instead. This is all fine up to, say, the size of a giraffe or elephant. But an elephant that runs for five minutes is in for a bad time. Vehicles are mostly empty space and skin, so they have different sorts of scaling problems.
  - pyuser583 5y ago
    Does that apply to cold blooded animals as well?
    - ncmncm 5y ago
      Differently. Actually expending energy produces waste heat, and they don't have mechanisms to speed up shedding it. A big lizard can run only a very short distance before overheating. Galapagos iguanas discovered swimming, and so can be more active than other big lizards.
      - ncmncm 5y ago
        The only land animals that have perfected long-distance running are humans and pronghorn antelope (which are really a kind of giraffe). Of course the birds have us beat all to hell, no matter which way you look. Fruit bats would be impressive if not for the competition from birds.

emteycz 5y ago

The height of trees is limited by the physical limits of water transport.

pyuser583 5y ago

“The surface is not large enough to transport all the heat away from the body” Can you explain that a bit more? I don’t understand.

cmyr 5y ago
As a body increases in size, the surface area increases as a square but volume increases as a cube. The more volume, the more heat, and after a certain point your available surface area is no longer adequate to vent that heat. Another example of a similar principle applies to insects: they don’t have lungs, and absorb oxygen directly through their skin. In earlier eras of earth’s history, there was much more oxygen in the air, and so insects could be much larger, because the same amount of surface area could absorb enough oxygen to fuel a larger number of cells.
ncmncm 5y ago
Look up "square-cube law". It governs everything about animal size. But not vehicles, so much. The principle is that 2x size, i.e. 2x length, 2x width, 2x height, gives you 8x volume and, for animals, mass. All that mass has to be kept fed and aerated, and produces heat. But the surface area didn't go up by 8x. It only went up 4x unless you changed the shape a lot. You probably can't get skin to shed heat 2x as well, so you have to be careful not to produce 8x as much heat, instead. This is all fine up to, say, the size of a giraffe or elephant. But an elephant that runs for five minutes is in for a bad time. Vehicles are mostly empty space and skin, so they have different sorts of scaling problems.
- pyuser583 5y ago
  Does that apply to cold blooded animals as well?
  - ncmncm 5y ago
    Differently. Actually expending energy produces waste heat, and they don't have mechanisms to speed up shedding it. A big lizard can run only a very short distance before overheating. Galapagos iguanas discovered swimming, and so can be more active than other big lizards.
    - ncmncm 5y ago
      The only land animals that have perfected long-distance running are humans and pronghorn antelope (which are really a kind of giraffe). Of course the birds have us beat all to hell, no matter which way you look. Fruit bats would be impressive if not for the competition from birds.