Modulus of elasticity is the relationship between applied stress, and strain.

If you try to bend wood by applying force to it, you are applying a stress, and the amount that it bends is called the strain. 1.8 million PSI is not actually that high of a modulus of elasticity, considering steel's is more like 30 million PSI.

Basically it tells you that wood is resistant to being deformed - but steel is significantly more resistant to being deformed.

OP might be confusing a high elastic modulus with a high [yield](https://en.wikipedia.org/wiki/Yield_(engineering)) point. In this case, since wood is a relatively stiff material, it will yield long before it deforms by very much (here's a table with yield strengths for wood boards).

To rephrase for OP: the elastic modulus tells you how much wood deforms, but it doesn't tell you anything about when it will bend out of shape permanently or break. A wood board can't support 450 cars, but not because it gets squashed, because the load exceeds the yield strength of wood.

This. The modulus of elasticity is the force need to stretch something (hypothetically) 100% . Most things cant stretch 100% so you stretch it by say 1% and multiply the result by 100

So does that mean that it would take 1.8 million PSI to stretch the wood to double its length; however, it would yield long before that?

Modulus of elasticity is a measure of how much something stretches when a force is applied provided you don’t stress it beyond its elastic capacity. It often correlates with strength, but not always.

To calculate how much something will stretch under a force:

Extension = Force x Length / (E x Area)

Wood has a decent modules of elasticity for its weight, but it’s E is lot less than most building materials. Something like 2-8% that of steel depending of species.

Pretty much, yes

Off the top of my head, I dunno how much sooner, but the "double its length" is spot on

Which is also why we have 350,000 ton steel sky scrapers instead of 1 million ton stacks of wood

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