Pendulum physics is used to describe the swinging motion of a pendulum that is caused by gravity. To create a pendulum, a weight, called a bob, is hung from a fixed point, called a pivot. By pulling the pendulum back and letting go, it will swing back and forth due to the pull of gravity and the tension along the string or wire that the weight is hung from. The movement continues as a result of inertia.
According to the basic law of inertia, whether a body is at rest or in motion, it will continue in that state unless it is acted upon by an external force. In the case of pendulum physics, the pendulum will continue to swing unless an external force acts to stop it. Since no external forces are acting on it, it can continue to swing indefinitely through the same arc.
The action of a pendulum is a good example of the conservation of mechanical energy. This law of physics states that the energy within a system always remains constant. In other words, the sum of the energy is always the same and energy cannot be created or destroyed. There are many different types of energy states that an object can be in, such as kinetic, potential, chemical, nuclear and thermal. Potential and kinetic, or moving, energy states are the ones that are measured and observed in pendulum physics.
When a pendulum is swinging, its energy state changes based on where in the arc the bob is, but what remains the same is the sum total of the bob’s potential and kinetic energy — in other words, the energy is conserved. At the pendulum’s highest point, it has no speed and all the energy in the system is potential. As it falls through the arc, the bob gains speed and kinetic energy while losing potential energy. Once it passes through the bottom of the arc, it begins to slow and loses kinetic energy while gaining height and potential energy. Although the kinetic and potential energy vary, pendulum physics measurements show that the total remains the same at all points in the arc of the pendulum.
In pendulum physics, air resistance and friction are assumed to be non-existent on the bob. Since the energy of a pendulum system is conserved, it is said to have perpetual motion, which can continue indefinitely as long as no energy is being lost to other objects or surroundings. The fact that a pendulum continues to swing in the same fashion over time is why it was used in clocks to keep time, and was initially used to take measurements of gravitational force.