Consider the average force exerted by a hammer striking a nail, which is around 100 pounds. The sharp nail tip has a one-hundredth of an inch square area. So the pressure exerted by the nail tip on the board is 100 pounds divided by 1/100 square inch, yielding an astounding 10,000 pounds per square inch! This is more than enough pressure to crush any human bone. The nail enters the wood at a forty-five-degree angle and comes out perpendicular, so it takes up only half of the total surface area of the board. Thus, the pressure per unit area is twice as great as if the nail were flat against the board. However, since we are dealing with a very small object, the actual pressure per unit area may be higher than this estimate because there is less space between the atoms that make up the nail and those that make up the board. When you hit a nail with a hammer, the force you exert on it is equal to the weight of the hammer times its distance from the nail head to the end of the handle. In this case, the weight of the hammer is 100 pounds and the distance is 20 inches. Therefore, the force you exert on the nail is 100 x 20 = 2,000 pounds. This calculation assumes that you use a regular hammer. If you use a sledgehammer, the force you can exert on the nail will be even greater.