Energy makes things happen. It makes a thing able to move, or causes something else to move. There are many forms of energy. Examples of energy are light, electricity, and heat. Light travels in waves. The biggest source of light energy is the sun. Heat energy is caused by the movement of the atoms and molecules in an object. The atoms in a hot object move faster than the atoms in a cold object. Electrical energy comes from atoms and electrons. Electrons have electrical charges which move in a path. Lightening is an example of electrical energy. Energy has the ability to move or transfer heat. Energy can be taken from one thing and added to another, but it cannot be destroyed. Mechanical energy is released by the working parts of a machine. Chemical energy is the energy stored in molecules. Chemical energy is released when the atoms in molecules are pulled apart. An example of chemical energy would be burning wood at a campfire. Nuclear energy is produced in nuclear reactors by the splitting of atoms.
There are two main types of energy. Potential energy is stored, or possible, energy. An example would be the energy in a roller coaster car at the top of the first hill. Kinetic energy is energy in motion. An example would be the same roller coaster car speeding at the bottom of the hill.
Light and Sound
Light and sound are both forms of energy that travel in waves. Light comes originally from the sun. Light can travel through space. Sound travels through a substance that has molecules which are able to move around. Light travels at 186,000 miles per second. Sound travels more slowly, between 1,083 and 1,115 feet per second in air. This is why we see the lightening before we hear the thunder.
Light waves travel in straight lines. The top of each wave is called the crest, and the bottom of each wave is called the trough. The distance from one crest to the next is called the wavelength. The height of a wave is its amplitude. A larger amplitude, creates a brighter light. It is called reflection when light rays bounce off shiny objects, like mirrors. Light changes speed when it passes through substances like water. The light rays slow down and bend. This is called refraction. Color is caused by the wavelength of light. Some colors cannot be seen. The colors red, orange, yellow, green, blue, indigo, and violet are the bands of color called the light spectrum. At the red end of the spectrum are infrared rays, microwaves, radar, television, and radio waves. At the violet end are ultraviolet, X-rays, gamma rays, and cosmic rays. Light waves are a form of electromagnetic radiation.
A laser beam is a beam of pure light, with waves that are all the same length. This creates a beam which is narrow, but very powerful. Lasers are used in the medical field to cut and repair tissue. The word laser stands for light amplification by stimulated emission of radiation.
Sound is made by vibration of objects. When matter moves backward or forward it vibrates, and produces sound. The molecules around it vibrate and set up a sound wave. If these waves reach your ears, bones inside your ears vibrate, a message is sent to your brain, and you hear the sound. Our vocal cords vibrate when we talk or sing.
The amplitude (height) of sound waves determines its loudness. Sound is measured in decibels. The softest sound that a human can hear is zero decibels. Because of the large range of intensities over which the ear is sensitive, a logarithmic (non-liner) scale is used to express loudness. Therefore 100 decibels is not twice as loud as 50 decibels. Sounds of 140 decibels or more can damage the ears. Normal conversation is at about 60 decibels. The frequency of a sound wave is the number of waves that pass by in a second. The higher the frequency, the higher the pitch. Low-pitched sounds have longer wavelengths and lower wavelength frequencies.
Electricity and Magnetism
Electricity is the movement of electrons (tiny particles) and the energy they release. The nucleus of every atom is surrounded by one or more electrons. Atoms have the same number of electrons as they have protons (parts of an atom). This makes atoms neutral, not electrically charged. But electrons can be rubbed off and moved to other atoms. This movement of electrons causes electricity. An atom with extra electrons has a negative charge. An atom with missing electrons has a positive charge. An electric current is a flow of electric charges, pushed along by a force. Electrical charges are controlled by making them flow in circular paths. A circular path of electrical charges is called a circuit. All circuits must have a source of energy. This could be a battery. The electrical energy flows through insulated wire, it powers a machine, and then flows back to the source of energy.
There are two kinds of current. Direct current (DC) flows in only one direction. Alternating current (AC) changes its direction of flow at regular intervals.
Electricity moves through some materials better than others. Metals are good electrical conductors. Water is also a good conductor. This is a good reason not to go swimming during a storm. Insulators are used on electric machines for protection. Plastic is a good insulator. All electrical wires and panels are covered with plastic or rubber.
A magnet is any solid substance that attracts iron or steel. Magnetism is caused by the electrical charges of electrons. The electrons around an atom spin in no special order. This changes when an object is magnetized. Then all the electrons are lined up. They pull together magnetically in opposite directions. This action creates a magnetic field. Each end of a magnet is called a pole. There is a north pole and a south pole in the magnetic field. Magnets may repel or attract each other. Opposite poles attract one another. Like poles repel each other.
Magnetism and electricity are closely connected. One can produce the other. An electromagnet consists of a coil of wire wound around a piece of iron. When an electric current flows through the coil, the iron becomes a magnet. The electromagnet loses its magnetism when the current is turned off. Microwaves are a form of shortwave electromagnetic radiation. Dynamos are generators that turn mechanical motion into electrical current. A wire coil is wound between the poles of a magnet. This motion in the magnetic field produces electricity in the wire. Microwaves are a form of shortwave electromagnetic radiation. They are used for communication, and also microwave ovens.