Science Buddies: "Ask an Expert"

My idea is that, if a nail is suspended in space and a cosmic hammer applies a force to the top of the nail, then the force will race downward through the tiers of atoms. Would the decreasing mass per layer of the nail's atoms cause an increase in the acceleration of the atoms at that tier? And when the force reached the last atom at the pinnacle of the nail, would the last atom act against the electromagnetic constraints that hold that atom to the others around it? Causing a kind of temporary expansion. The way I imagine it is like a ripple effect that becomes more intense as it progresses, like a wave approaching the beach

I recommend that you read up on Newton's three laws of clasical motion. I don't think you are considering enough factors to predict the actual result.

I then recommend that you imagine "cutting the head off the nail" and model the shaft part of the nail as a cylinder of uniform cross section and the point as a cone. This will eliminate a significant modeling challenge of dealing with the material and boundary changes between the "head" and the shaft. note: The head is usually formed by an impact in some mold or fixture so the material is definitely not uniform in the head and at the top of the shaft.

If you then take that simplified mode of the nail and treat it as a finite number of elements by imagining sections as if you sliced the nail into multiple pieces perpendicular to the major axis. You can then assign some mass to each section, some elasticity and plastic force limits to the sections and the connections between the sections.

Assuming the nail is stationary in space prior to the impact will simplify the model.

The impact force on the top of the nail floating in space will not immediately be felt by the the point because of Newton's first law but will affect each modeled section in turn as a wave traversing down the cylinders. The end result of what happens to each cylinder will depend on the plastic force limits (where the metal deforms) and the elasticity will determine what third law reactionary force waves will start traversing up the nail.

IMO: This model is not significantly different from what happens to a nail whose pointed straight down into a sufficiently thick and dense a block of uniform foam the surface of the earth. Only the boundary conditions at the point will differ and the block of foam will have to be modeled and as long as the force is insufficient for the nail to fully penetrate the block of foam, no other boundary conditions will occur. In other words, you can actually do the experiment and determine the properties of the actual nail used assuming you have accurate enough measuring tools to determine any plastic deformations.

If you actually want to do the experiment, you might consider using a pneumatic "finish" nailer that uses uniform cross section wire nails.