Forms of Energy

■ Chemical energy is the form stored in the bonds of chemical substances. When chemical reactions occur that rearrange the atoms of the chemicals in a certain way, the potential energy is unleashed and becomes kinetic energy, or energy in action.

For example, some of the energy in the foods you eat is eventually converted into the kinetic energy of your moving arm. However, food fuels cannot be used to energize body activities directly. Instead, some of the food energy is captured temporarily in the bonds of a chemical called adenosine triphosphate (ATP) (ah-den’o-sen tri’Wfat). Later, ATP’s bonds are broken and the stored energy is released as needed to do cellular work. Chemical energy in the form of ATP is the most useful form of energy in living systems because it is used to run all functional processes.

■ Electrical energy results from the movement of charged particles. In your home, electrical energy is found in the flow of electrons along the household wiring. In your body, electrical currents are generated when charged particles called ions move along or across cell membranes. The nervous system uses electrical currents, called nerve impulses, to transmit messages from one part of the body to another. Electrical currents traveling across the heart stimulate it to contract (beat) and pump blood. (This is why a strong electrical shock, which interferes with such currents, can cause death.)

■ Mechanical energy is energy directly involved in moving matter. When you ride a bicycle, your legs provide the mechanical energy that moves the pedals. » Radiant energy, or electromagnetic energy (e-lek”tro-mag-net’ ik), is energy that travels in waves. These waves, which vary in length, are col-
lectively called the electromagnetic spectrum and include visible light, infrared waves, radio waves, ultraviolet waves, and X rays. Light energy, which stimulates the retinas of our eyes, is important in vision. Ultraviolet waves cause sunburn, but they also stimulate our body to make vitamin D.