Flow of Energy
Heat is the flow of energy from a cold object to a warmer one. Heat can be transferred by convection, conduction or radiation. Convection is hot gas or liquid rising above cold gas or liquid because it is less dense. Conduction is the transfer of heat through direct contact. Radiation is heat being emitted from a hot object or a reaction. If you feel the heat coming off a fire, you experience radiation. If you hold your hand above the fire, you will feel additional heat through convection. If you touch a hot object, you will feel even more heat through conduction.
Endothermic and Exothermic Reactions
Endothermic reactions are reactions that absorb heat from their surroundings, like chemicals that react when heated. Exothermic reactions are reactions that give off heat, like those that combust or catch fire when combined.
Kinetic and Potential Energy
Kinetic energy is the energy that an object has when it is in motion. Potential energy is the energy that an object has because of what it is capable of doing. If an object is in a high place, it has potential energy. As it falls, it loses potential energy at the same rate that it gains kinetic energy. This is called conservation of energy.
Chemical energy is potential energy that can be converted to other types of energy by a chemical reaction. The chemical energy of food can be converted to kinetic energy (movement) by cells in the body. Combustible materials contain chemical energy that is given off when they burn.
Mechanical energy is the sum of kinetic and potential energy. Because of the law of conservation of energy, mechanical energy of an object remains constant as it moves. A pendulum has potential energy when it swings upward. It then has kinetic energy when it swings downward and is moving fast. It always has the same mechanical energy.
Sources of Energy
The environment contains many sources of energy that people can harness to create electricity or do things.
Heat radiates from the sun and is absorbed in solar panels. It is an example of a method of energy production that reduces pollution. It is sustainable, but relies on there being sunlight.
Oil, Coal and Natural Gas all contain chemical energy. They are mined or drilled from the Earth and burnt, producing energy. Fossil fuels may not be sustainable because there is a finite amount of them. They also produce pollution.
In a nuclear reactor, splitting an atom gives off heat in a reaction and the energy is harnessed. Nuclear energy is sustainable, but does produce some nuclear waste. The major reason nuclear energy is not more widespread is because of the threat of accidents, like the ones at Chernobyl (1986) and Fukushima (2011).
Waves transfer energy. Electromagnetic waves transfer energy by vibration of electric and magnetic fields. Water waves transfer energy by moving particles of water. Sound waves are movement of particles transmitting sound. A wave has a wavelength, or the distance between waves. Amplitude is the height of a wave. Frequency is how many waves occur in a time frame. Higher wavelength means lower frequency.
Electromagnetic energy is transmitted in waves. The electromagnetic spectrum shows waves of varying wavelength. The higher the frequency (lower wavelength) the more energy a wave can transmit. At the high energy end of the spectrum are gamma rays: energy traveling through space. At the low energy end of the spectrum are TV and radio waves that pass through the air around us unnoticed. Only a small portion of the spectrum is light waves visible to us.
Roller Coaster Photo: University of Richmond; Pendulum Photo: User thedailynathan/Wikimedia; Electromagnetic Spectrum: Simon Baier