## It’s time to hammer home the hypotenuse

Is it better to drive nails with many light blows or with fewer heavier blows? I suppose that depends on what stage of the drive you are in, what kind of hammer you are using, why you are driving nails, what kind of wood and nails you are using, and for that matter, your time frame.

Speed and efficiency are sometimes very different things. For example, theoretically, you can hammer faster harder. But if you bend the nail, or hit your thumb, it may actually take you longer. So the answer to the original question could be yes, no or maybe. As always, further research is needed.

I didn’t know until recently that not all percussive tools, scientific jargon for hammers, are alike. Oh, I know there are claw hammers and ball-peen hammers of numerous sizes and configurations. But hand tools were never scientifically designed. They were just made the way they are because they worked best that way. I mostly have chosen to use claw hammers over others because they are like pencils. They have an eraser on the other end for my mistakes.

I just bought a new percussive tool made specifically for hammering frets into a fret board of a stringed instrument. It’s flat on both surfaces only with different metal faces. It seems odd that one would need a special hammer just to fret. My wife does that pretty well with no hammer whatsoever.

Once, in my distant past, I helped a roofer put shingles on a roof. He could put the nail down point first, move the hand holding the nail, strike one blow of the hammer with the other hand, and be done. I tried to do that myself ... once. That’s how I discovered the principle that a given force, or motion, is actually the result of two independent components.

If one throws a rock straight into the air while riding a bicycle forward, the rock will fall to the earth beside you as you travel forward. This is because the rock will be traveling forward at the same speed you are while it is ascending and descending from the force of your throw. I once demonstrated this quite well by having the rock successfully land directly on my head.

So every motion can be described as the result of two other motions. The hammer exerts a force directly down on the nail. However, it also has a force that is exactly perpendicular, or sideways. Hence one force is driving the nail downward, while the other force is driving the nail sideways. Collectively, the two forces form the vertical and lateral arms of a right triangle, and the resulting force is the hypotenuse.

If the hypotenuse is efficient, the nail is mostly driven downward. If the sideways force is excessive, the nail will be bent, and/or the thumb mashed. The bent nail requires the use of another tool called the fulcrum. One is conveniently attached to the opposite side of a claw hammer. Fixing the mashed thumb may require other tools, too, such as a heated needle (a type of wedge) and/or bandage (another type of percussive tool) to fix. (In the interest of space, quasi-scientific explanations of these other tools must be reserved for later columns).

The center of the hammer head is not necessarily the best place to strike the nail. Each hammer head has a sweet spot where the momentum transfer is maximum. Why? Because the hammer does not come straight down but swings in an arc, like a baseball bat. I am told you can calculate the exact “sweet spot” of a mass swung in an arc. You can do it. I don’t intend to. Considering the small size of a hammer head, my main problem is still swinging it accurately enough to actually hit the nail, and not my thumb.

Frequent, light blows are less painful.

Gary McCallister, mccallis@ coloradomesa.edu, is a professor of biology at Colorado Mesa University.

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