Question

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Consider a model steel bridge that is 1/100 the exact scale of the real bridge that is to be built.

If the model bridge weighs 50 N, what will the real bridge weigh?

If the model bridge does not appear to sag under its own weight, is this evidence the real bridge, built exactly to scale, will not appear to sag either?

Answer 1

Since the model bridge 1/100 th the exact scale of real bridge, the dimensions of the real bridge will be 100 times that of the model. SO the volume of the material of real bridge will be 1000000 i.e 10⁶ times that of the model. So the real bridge will weigh 5 x 10⁷ N.

No the evidence that the model bridge doesn't sag under it's own weight is not an indication that the real bridge will not sag either, because the environmental loads are not considered for the model and also the rigidness if model is more due to it's small size.