Measuring time is a necessity of life. Whether time is long or short, relying solely on intuition is not accurate. Objectively, we need a "ruler" to measure time. For example, the speed of the Earth's rotation changes very little, and when the requirements are not high, it can be considered constant. Using the time of one complete rotation of the Earth as a unit of measurement is a day and night. To further subdivide time, we need to find a shorter constant motion as a measurement standard. As early as the 16th century during the Renaissance in Europe, Italian science master Galileo accidentally noticed that even though the swinging amplitude of the pendulum in the church was getting smaller and smaller, the time it took to swing once was always constant. This discovery was very important, as it provided a simple method of measuring time. As long as we find a way to use a pendulum to drive the minute and hour hands, we can create an accurate mechanical clock.
However, to make this mechanical clock using pendulums a reality, we must overcome a huge challenge. During the swing of the pendulum, it will inevitably be disturbed by various resistances, such as friction in the bearings and air resistance. Due to the existence of these resistances, the swinging amplitude of the pendulum will gradually decrease, and finally the amplitude will decrease to zero and stop completely. To solve this problem, clever craftsmen invented the "escapement mechanism". This mechanism consists of an escapement wheel and an escapement fork. The escapement wheel is connected to the heavy hammer, and the escapement fork is connected to the pendulum. After lifting the heavy hammer to a high position and letting it go, the heavy hammer will slowly fall under the action of gravity, simultaneously impacting the escapement fork. The ingenious part of the escapement mechanism is that no matter which direction the pendulum moves, the direction of the impact is always consistent with the direction of movement. For each swing of the pendulum, the energy lost due to resistance can be replenished by the impact of the escapement wheel, so the swinging amplitude of the pendulum will not decay. As early as the Song Dynasty, this ingenious escapement mechanism had been applied in the water-driven "Water Transport Instrument". In 1656, Dutch scientist Huygens designed the first pendulum clock equipped with an escapement mechanism.
Physics defines the product of the force acting on an object and the distance the object moves as "the work done by the force on the object". If the direction of the object's movement is consistent with the direction of the force, the work done is "positive work". The effect of positive work is to increase the object's energy. If the two directions are opposite, it is "negative work", and its effect is to reduce the object's energy. During the swing of the pendulum, the friction force is in the opposite direction of the pendulum's movement, while the impact of the escapement mechanism is in the same direction as the pendulum's movement. When the negative work of friction is exactly compensated by the positive work of the escapement mechanism, the energy of the pendulum will remain constant, and the clock will continue to swing. The energy lost by the pendulum is not lost forever, but converted into another form of energy in the form of heat. The energy replenished by the escapement mechanism is not created out of thin air, but comes from the descent of the heavy hammer. When the heavy hammer descends to the lowest point, it needs to be pulled up by human effort before the clock can continue to run. There are many ways to replenish energy. Using a tightened steel spring to replace the lifting of the heavy hammer is a more common method. In the objective world, energy cannot be created or destroyed out of thin air, but can only be converted between different forms in different objects. This is the universal law of conservation of energy in nature.