On energy and its nature.
Energy is a scalar quantity that can perform work in various forms. It has many forms including heat, motion, and light. The law of conservation of energy states that “energy can never be created or destroyed” but it can be transformed into other types of energy. However, Einstein’s equation e=mc^2 is a formula where e is energy, m is mass, and c is the speed of light. Mass can be converted to energy, and this equation shows how. The energy produce will be equal to the mass of the object (usually a neutron) times the square of the speed of light. The only occurs in situations of high heat and pressure, such as on the sun where nuclear fusion turns mass into energy, or even here on earth by nuclear fission in nuclear power plants and atom bombs.
Mechanical energy has 2 forms, kinetic and potential. These kinds of energy are what cause motion in physical objects. Potential energy can be defined as stored energy, and kinetic energy as the energy possessed by an object’s motion. In potential energy there are further divisions, such as gravitational potential energy, elastic potential energy, and electric potential energy. Thermal energy, or heat, could also be considered mechanical, although the motion it causes is mostly on the atomic level. The total amount of thermal energy, or heat, in an object is simply a measure of the movement of its atomic components. The hotter an object, the faster the atoms are moving. Thermal energy can cause motion on a larger scale as well, such as when water is heated to steam, which then rises due to its lower density. Steam can be used to turn turbines and do work.
Waves are a way to transport energy. Mechanical waves need a medium in which to move, and electromagnetic waves do not. Sound waves, ocean waves, and shock waves are examples of mechanical waves. In mechanical waves, energy is moved through a medium, but returning the medium to its original resting position once it has left. A mechanical wave moving through a solid medium, such a rope will cause the whole rope to move at one time or another, but once the wave has passed through, the rope returns to its original position. When one end of the rope is fixed, the energy doesn’t transmit, it only reflects. The loss of energy and seizing of the wave is only caused by the air around the rope that gets moved during the motion of the wave, unless some energy is lost to the motion of the fixed end, such as a loose ring stand.