Why I can't melt a piece of 2"x4" steal with a welding torch if I don't concentrated it on a small area?

Question

Was the Jet Fuel and fire concentreated only on one small area of the buildings on 9/11?

Answer 1

I believe the heat dissipation is an inverse squared. If you move a centimeter away, the heat is a 1/4 of its original strength. Take that concept, couple that with surface area. The larger the surface area more heat you would need to make it melt. That is why a needle will pierce your skin if you use the same force and a knife won't. The force applied over a small area is more devestating than one applied over a large area.

As for the 11/9 quesiton, i don't think such a simplistic analysis will work. As you pointed out, i presumed the metal wasn't anything special. Buildings have different materials, the heat has to go through different material, the loss rate differs, the air currents caused by the crash, the sprinkler system, there are quite a few variables that you have to take into account to answer the 11/9 question rather than drawing an analogy between metal and heat and the plane crash.

Heat is energy here, which can be made into force.

Answer 2

If you heat a small spot to a higher temperature with a torch than the bulk because it takes time for the heat to diffuse away from the hot spot via thermal conduction. So, the heat just builds up until it melts. If you heat a large piece with a big flame (or move the flame around), a large area of metal is exposed, so the heat loss rate due to radiation and air convection with equal the heat input rate before the temperature gets too high. Of course, how hot this is depends on the magnitude of the heat input. A plane load of fuel burning up in a few minutes releases an awful lot of heat quickly, so it was able to heat to the point of softening over large area of the structural members of WTC.

Answer 3

This depends on the size of the flame and the size of the piece of steel.

There are 2 competing effects - heat added by the flame, and heat lost from the steel by conduction to areas away from the flame, and ultimately by convection to the air.

If you have a small flame and a relatively big piece of steel, you need to focus enough heat at one spot so that its temperature rises above the melting point of steel, even though heat is being conducted away.

If at the other extreme, the fire is much larger than the local steel structure, the structure will approach the flame temperature. The melting point of common steel is well below the flame temperature of hydrocarbon air fire. Thus the steel melts.