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.
When the wave meets the fixed end, it reflects and inverts. If the wave was moving along the top of the resting point of the rope, it would reflect back along the bottom. If the end of the rope is free to slide up and down, the wave still reflects back, but will remain on the same side of the medium's resting point. The speed of the wave can be increased or decreased by the tension in the rope, because changing the tension changes the elasticity. The tenser the rope, the faster the wave will move, due to the ropes increased nature to return to its original resting point. Mechanical waves have 2 forms, longitudinal, and transverse. Sound waves are longitudinal, and the wave vibrates parallel to the direction of the waves motion, whereas the wave in the rope or on the ocean is transverse and vibrates perpendicular to the motion of the wave.
Electromagnetic waves do not need a medium in which to transfer energy. This is because they are self propagating waves, which means that the electric and magnetic forces produce the other. If the electric energy propelled the wave along a vertical plane, it would produce a magnetic wave that propelled it along a horizontal plane. These waves produce each other, and for the most part, generate their own medium in which to move through. All electromagnetic waves move at the speed of light, 3.0x10^8 m/s, in a vacuum. When they enter a medium they slow down, but only slightly. The speed of the electromagnetic wave decreases with the increase in density of the medium. There are multiple kinds of electromagnetic waves, they are separated by their wavelengths, and since their speed does not change between them, the smaller wavelengths carry more energy than the longer ones. The shortest wavelengths in the electromagnetic spectrum are cosmic and gamma rays, whereas the longest are radio and microwaves.
Sound waves are generated by the compression and expansion of air as the energy moves through it. Sound waves spread from a central point in a spherical motion, that is, every direction. The speed of a sound wave is determined only by the medium in which it is moving through. The more elastic the medium, the faster the sound wave can move, and also the longer distance it can travel. Steel is a very elastic material, and sound can move through it very rapidly. The wave can travel a longer distance, because the atoms in the medium are already so tightly packed together, that less energy is wasted in colliding the atoms together, to carry the wave. Since water is denser and more elastic than air, it can carry sound waves further than in air. For instance the blue whale's calls can be heard up to 1,000 miles away by its prospective mate. When a sound wave comes to a medium boundary point, the differences between the mediums determine how much of the energy is reflected back, and how much is transmitted. When a sound wave moves into a more dense medium, more of the energy gets reflected than transmitted, when it moves into a less dense medium, more energy is transmitted than reflected.
