What would be impossible to build and why?

[monty28]

why are guns metal? why are bridges made the way they are? why do we not make double decker lorries? this is my thinking... you follow?

 

[russ_watters]

Not really...

 

[monty28]

ok... what about - what would you like to make but cant?

 

[Averagesupernova]

Certain people in my life go away? LOL
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No seriously, things are put together the way they are for a number of reasons. Sometimes it's economics. Sometimes it's safety. Sometimes it's convenience. Sometimes it's simply because there is only one way to put something together and still have it work or stay in once piece due to limitations in materials used. As we come up with new materials, things change.

 

[brewnog]

Most things are built the way they are because that is the cheapest way of achieving the customer specification.

What purpose would double decker lorries serve, except to reduce the amount of things you can carry on one? Common sense is usually a significant driver in why things are built the way they are. Why give a lorry two decks when it performs its function better with one?

 

[Danger]

I must point out two exceptions to that, Brewski, although both are special-purpose instances. Flatbed semi container trucks could be considered 'double-decker', since they usually carry one container on top of another. That's a bit of a stretch, but acceptable. The other is auto transports, such as those that deliver from the factory to the dealerships. Those have two decks so as to double the number of cars that can fit on them.

Monty, guns are steel because until very recently that was the only material strong enough. They now have some that are made almost exclusively of various plastics. As far as I know, though, they still need a steel sleeve in the barrel to bite into the bullet for ballistic spin.

 

[Mech_Engineer]

why are guns metal? why are bridges made the way they are? why do we not make double decker lorries? this is my thinking... you follow?

It's impossible to build a 100% efficient machine,

You can't have a thermodynamic heat engine that is more efficient than the idealized Carnot cycle,

You can't make Gold out of Lead,

You can't close Pandora's Box once it's open...

However:

You CAN make a gun out of only ceramics,
EDIT: Well, 95% ceramics anyway

You CAN make bridges in an infinite number of configurations, just try and number how many different kinds there are,

You CAN make a double decker anything, but you CAN'T overcome cornering forces, center of gravity, or low bridges...