R

Renewable resource

Renewable resource: A natural resource that can be produced, regrown, or reused fast enough to keep up with how quickly it is used. Wind, tides, and solar energy, for example, are in no danger of running out and can be consumed by people virtually forever. In contrast, fossil fuels such as coal take millions of years to develop naturally and are considered nonrenewable.

Radiation

Radiation: Energy that travels in the form of a particle or a wave. There are many different types of radiation. Some types can harm people, while others are harmless and actually quite important to everyday life. Several common forms of radiation are classified as “electromagnetic radiation,” including radio and TV waves, X-rays, ultraviolet radiation, infrared radiation, and visible light.