You have two bridges that are identical, except that one is exactly five times bigger than the other...?

Question

...which bridge is stronger? why?

i think its the smaller one but im not sure at all

thanks! those answers helped a lot...! :)

Answer 1

the smaller one would be stronger, as it would not suffer as much tensile stress (or strain) per volume area..... all materials have a certain amount of pressure and stress they can withstand before buckling or deforming in someway, and is known as 'youngs modulus' (this is a ratio between the stress and strain limits of a material). the forces on a bridge that enginneers worry about are more often that caused by the bridges own structure than of vehicles and other things across it, such as the weight of the steel and concreate been pulled down between two supporting pillars by gravity, or the weight carried on suspension cables.

so even if the scale was increased 5 times, the limits of the material (steel for example) would not increase, the thicker the steel supports, the more spread the pressure (force over area) is, tru..., however, this is not sufficient enough to support the new weight load; for example... imagine a cylindrical steel support.... even if the scale increased 5 times, the forces would exceed the limits, the structure would be 5 times greater... but unless the limits of the material became 5 times greater... it would not hold....
....... i think.

hope that helps!

that psychics explanation!!!

Answer 2

The weight (mass,if we're going to be pedantic!) of an object is dependent on its volume. Volume is dependent on the quantity length cubed - if you have a square cube and double all of its dimensions, that is length, width and height, then the volume of the new cube would be 2x2x2=8 times as much as the original cube.

The capacity to carry load of an object is dependent on the material strength and the cross sectional area of the object. Given the same material, greater cross sectional area will carry more load. But cross secitonal area increase with the square of length - doubling the dimensions of a square would quadruple its area.

So if you have a beam or a stick, if you scale its dimension up by a factor of 2, then the weight would be 8 times what it was, while the carrying power would only increase 4 times. So relatively speaking, the bigger beam would be "weaker" than the smaller beam, all else being equal, since a greater proportion of its load capacity would be required just to carry its own weight.

Obviously it's a bit more complicated in a bridge. But the same principle applies.

This sort of disproportional scaling effect applies frequently in physics and engineering - scaling the physical dimension of something rarely equate to an exactly corresponding increase in its capacity/performance. And certainly not its cost!

Answer 3

The larger one is the most structurally secure in most cases. It really depends on the type of bridge. A suspension bridge is usually stronger over long distances but unsupported bridges are usually stronger when smaller.

Answer 4

I have to disagree with most of the posts here. If you double the span, the resulting bending stress quadruples. If you increase the span by a factor of 5, the resulting bending stress increases by a factor of 25.

Thus the larger bridge would have to be 25 times stronger.
The smaller is stronger!

Answer 5

The Stronger bridge is neither.

Due to the scales of each bridge, they both have positives and negative. The larger one will support more weight but will also have more traffic while the smaller one can hold less but will have less traffic.

Answer 6

they have exactly the same strength.
when you really do think about it, the smaller one is just a prototype of the bigger one. whatever happens to the smaller one should be expected to happen to the bigger one. if they weren't identical then you'd be correct in saying that the smaller one is stronger, but even that answer would be subjected to other factors.

Answer 7

The slenderness of the bridge increases with the span between supports. Slender structures buckle more easily than compact ones. Hence increasing the span reduces the buckling strength of the bridge.

Answer 8

Doesn't it depend on what it spans and what weight you will allow?

logic says the smaller one is less liable to break under certain pressure, while the larger one could be weakened by the load allowance... although on the surface, you'd assume they'd be the same.

I guess in usage though, it's down to stress factors and key stones... and not least, terrain on which your build.

Answer 9

the larger one is stronger. why?

think of it this way..a tooth pic compared to a twig that is bigger. it is clear that the twig can handle much more force/weight than the tooth pic. the same principle applies to the bridge whereby the thicker trusta and beams can handle much more stresses than the smaller bridge with thinner beams.

Answer 10

How can they be identical if one is five times bigger, in proportion to their sizes both will be equally strong