Motion and forces Study Guide

Newton’s Second Law can be stated in terms of momentum: the net force acting on an object is equal to the rate of change of its momentum. The law is formally written as F = (mv − mu) / t, where m is mass, u is initial velocity, v is final velocity, and t is the time over which the change happens. This approach is particularly useful when analysing impacts, collisions or any situation where momentum changes over time. The SI unit for force is the newton (N), and momentum is measured in kilogram metres per second (kg m/s). The equation shows that a larger force or longer time interval leads to a bigger change in momentum, linking the concepts of force, time, and motion.

Human reaction time can be measured using different methods, including the ruler drop test and computer-based tests. The ruler drop test involves one person holding a ruler vertically at another person's eye level, with the zero mark at the second person's thumb and forefinger. The first person drops the ruler without warning, and the second person catches it as quickly as possible. The distance the ruler falls before being caught is then used to calculate the reaction time using a specific formula. Computer-based tests often involve a visual cue appearing on a screen, and the user must click a button or key as quickly as possible. These methods allow for repeated trials to calculate an average reaction time, which helps improve the reliability of the results. Typical human reaction times range from approximately 0.2 to 0.5 seconds, though this can vary significantly due to factors like age, fatigue, distraction, and the presence of stimulants or depressants.