ewton’s second law is applied during the design of helmets. A helmet protects a person’s head in the event of a collision, such as one that may occur when playing sports. Scientists and engineers test the effectiveness of a helmet through a "drop test." In such a test, a helmet is dropped under controlled conditions, and data from the resulting collision with the floor are used to calculate the change in the helmet's acceleration and force. Currently, the most effective helmets contain polystyrene foam for padding. The padding functions to the amount of force a person experiences during the collision by the length of time over which the collision takes place. Scientists working to improve the safety of helmets typically work in specialized areas of expertise. This division of work makes the task of improving helmet design more effective because it allows each scientist to study a smaller, more manageable problem. For example, experts in might collect and interpret data from drop tests of existing helmet designs. Other scientists can then use these results to develop a new design that .