# Physics question momentum, energy, strength of steel, PSI etc

## Main Question or Discussion Point

1.) If a car is in a frontal crash test, and goes hurling into a steel wall for instance, what unit of measure is used to define the strength of the steel wall? For instance, is the resistance strength of the steel measured in tensile strength, yield strength or something else?

2.) Another example... if the car is traveling and its energy is measured in foot pounds [lbf / ft^2] or even in joules....and it smashes into the steel wall......how would the walls resistance to the cars impact be measured?

3.) Lets say, this steel is measured perhaps in yield strength (ksi or thousands of pounds per square inch) is the force per square inch where deformation exists in the steel.

How it this to be understood? Lets assume that an imaginary vehicle is so heavy/dense that it is capable of smashing through the steel impact wall. The vehicle is 10 feet wide and 5 feet high. How is the size and weight of the vehicle divided up against all those square inches of steel to allow a hole to form?

I guess what I'm trying to understand is if the strength of the steel is measured according to thousands of pounds per square inch, is that "single unit's" strength multiplied by the total area that the imaginary vehicle impacts it and smashes a hole in the steel?

What formula would be used to compute this?
This sprung from my kids homework (not a homework question in and of itself) and we're just trying to understand how this works in theory.

Hope this makes sense. Thanks.

Related Other Physics Topics News on Phys.org
With metals its not about resistance its about ductility. The ductility of a metal is how easy it is for the atoms to move, metals are ductile because they have delocalised electrons.

AlephZero