The hammer may be humanity's oldest tool, and its physics is surprisingly clever
Near Kenya's Lake Turkana in 2012, Sonia Harmand and Jason Lewis of Stony Brook University found a large cache of shaped stones used for bashing wood, bone and other rocks, dated to around 3.3 million years ago. No other tool has such definite archaeological evidence stretching that far back.
Those earliest hammers were simply stones held in the hand. Handles arrived much later: by about 30,000 BCE people were lashing stones to sticks with leather strips or sinew, which improved control and cut down on accidents. Some researchers even suspect that the planning, sequencing and timing needed for throwing, clubbing and hammering helped drive brain evolution in early hominids. A fast, accurate blow is a ballistic movement, planned before it starts because it happens too quickly to correct mid-swing, which is why striking takes more practice than tapping.
Mechanically, a hammer amplifies force. During the swing the head stores kinetic energy roughly equal to the arm's force times the length of the swing. When it hits something hard, the head stops over a tiny distance, so the stopping force is larger than the original push by about the ratio of those two distances. That is how an ordinary arm can bend steel or crack stone. Delivered energy is half the head's mass times the square of its speed, so speed matters far more than weight, which is the real job of the handle.
Handle length is always a compromise. Longer means faster, but also harder to aim and impossible in cramped spots; sledgehammers get long handles because they are swung in open space. Hickory and ash are favoured for wood handles because they soak up shock, while fibreglass resists rot but damps vibration less. Light titanium heads allow longer handles and bounce back only about 3 percent of their energy, against as much as 30 percent for steel.
Specialised forms abound, more than 40 types in all. Dead blow hammers hide sand or lead shot in a hollow head to kill recoil. In coal mines, refineries and chemical plants, where a spark could ignite gas, workers use non-sparking hammers of aluminium, brass or beryllium copper. Some upholsterers' hammers have magnetised faces for picking up tacks.
Source: Hammer
