The term global warming refers to Earth's slowly rising temperature, especially in the last 20 years or so. A major cause of global warming is air pollution from both cars and factories. Not all scientists agree that global warming is happening. Some say it is impossible to know if the climate is changing overall. After … Read more

A laser is a device that produces a beam of light and makes the beam more intense. A laser beam is very exact. It can travel a long distance without spreading out and losing its power. Laser light is unlike sunlight or light from a light bulb. To understand the difference, think of a crowded … Read more

Famous scientist Albert Einstein first suggested the idea of a laser in 1917. In the 1950s, scientists began making the idea work. American scientist Gordon Gould suggested the name laser in 1957. It was short for Light Amplification by Stimulated Emission of Radiation. The first working laser was built in 1960. It was built by … Read more

Space is a difficult place to be. You can't plug in a cord in outer space, so satellites need to take a power source with them. It's hard to get satellites pointed in the right direction because there's nothing to turn them with. Satellites need to work in the freezing cold of Earth's shadow as … Read more

Glass is made by melting silica, a chemical that comes from sand. At extremely high temperatures, silica melts and becomes liquid. Other substances are usually added to the melted silica to make the glass strong. In its liquid state, glass can be molded into different shapes. Glass was first made at least 4,000 years ago. … Read more

Today, ice covers Earth's North and South poles. These ice caps are called polar glaciers. During an ice age, the polar glaciers grow larger. At the height of an ice age, glaciers may cover as much as a third of the Earth. Canada, the northern United States, northern Europe, and northern Russia all get covered … Read more

Sunlight is a mixture of light of different wavelengths. Although we can see each as a separate colors, combined they appear to be white. As a ray of sunlight enters a raindrop, its color components are bent, or refracted at different angles and reflected off the raindrop's inner surface. Then as it leaves the rain … Read more

An understanding of the mode of transmission of bacteria and other infectious agents is extremely important from a public health perspective, because interrupting the chain of transmission is an excellent way to prevent infectious diseases. The mode of transmission of many infectious diseases is "human-to-human" but infectious diseases are also transmitted from nonhuman sources such … Read more

People get infectious disease when microorganisms overpower our host defenses, i.e., when the balance between the organism and the host shifts in favor of the organism. The organism or its products are then present in sufficient amount to induce various symptoms, such as fever and inflammation, which we interpret as those of an infectious disease.  … Read more