By observing a weight suspended on a string, Galileo noticed that the weight, when pushed, swings from its central resting position to one side a certain amount and then to the other side the exact same amount. Also, the timing of these swings from one side to the other was precisely regular. This made it possible to calculate time with exactness and led to the invention of mechanical clocks with swinging pendulums driving the gears. Later, a similar natural law was proposed by Isaac Newton which stated that every action has an equal and opposite reaction.
In human psychology, a pendulum effect has been noticed in relation to moods and emotions. An extreme case of this would be bipolar disorder, which causes a person to swing from intensely happy feelings to the opposite side into deep depression.
In politics it has been observed that people tend to align themselves to what is called either the political left, right, or center. A general description of these terms is that the political left refers to liberal values, the political right refers to conservative values and that the center is a blend of both these viewpoints. The pendulum effect occurs in democratic governments when the population elects a leader representing the polar-opposite views of the preceding leader.
In the media, celebrities are often subject to the pendulum effect. A sudden rise in popularity can be followed by a public backlash followed by another rise in popularity. An example of this can be seen in John Travolta's acting career, which began strong in the 1970s, suffered public neglect in the 1980s, and was revived again in the 1990s.