What does 100 look like? Sound like? Feel like? In this video from Curious George, explore the many ways to measure 100 things.

In this video segment from Cyberchase, the CyberSquad replaces a piece of track to get the Madre Bonita Express to the Mother's Day harvest.

Examine this graph from FRONTLINE/NOVA: What's Up with the Weather? Web site to see dramatic increases in three greenhouse gases over the last two hundred years.

This video adapted from the Valdez Museum & Historical Archive, explores what happened during the Great Alaska Earthquake of 1964 through original footage, first-person accounts, and animations illustrating plate tectonics.

This visualization from NASA shows global rainfall patterns over a 22-year span. It incorporates data from a combination of remote-sensing and ground-based sources.

This Wide Angle video features the women of Rwanda who have emerged as outspoken leaders and the great strides they have made toward rights and equality.

This animated essay from the American Experience Web site explains the difference between alternating and direct electric current and offers in-depth explanations about the role played by a battery, light bulb, wire, and generator. Grades 6-12.

This video segment from Between the Lions stars Theo the Lion reading aloud the story of Abiyoyo, a South African tale packed with suspense, heroic characters, and new words.

This video segment adapted from First Light explains why the highest peak in the Pacific, Mauna Kea, is an ideal site for astronomical observations. Featured are new telescope technologies that allow astronomers to explore the universe in more depth.

This segment from Swift: Eyes through Time traces the history military officers and engineers discovering a strange phenomenon in the sky that astronomers now know are gamma-ray bursts.

Add acidity to a healthy lake and see what happens to the plants and animals in this interactive activity adapted from EcoKids.

In this video segment, the ZOOM cast demonstrates how to use cabbage juice to find out if a solution is an acid or a base.

In this interactive activity from the ZOOM Web site, search for chemistry clues and experiment with acids and bases in a virtual kitchen.

In this video segment adapted from ZOOM, two cast members demonstrate what happens when vinegar is added to baking soda inside a container. The resulting chemical reaction produces enough carbon dioxide to launch their paper rocket skyward.

Recommended for: Grades K-5

A car propelled by the reaction between lemon juice and baking soda has more in common with rockets and jet aircraft than one might think. In this video segment adapted from ZOOM, two cast members demonstrate the power of rocket-propelled vehicles and how to exploit the force produced by the carbon dioxide gas. Grades 3-8.

It would seem that bottles of lemon juice and rockets have only their basic shape in common. However, as two cast members from ZOOM demonstrate in this adapted video segment, when baking soda is added to the mix, a plastic bottle can act very much like a real rocket. Grades 3-8.

Finches on the Galapagos Islands have evolved to exploit almost every possible niche. This diagram shows the range of food sources available on the island and the different beak shapes adapted to exploit each of them.

Our brains control every movement we make. Most of us take for granted our ability to pick up a cup or change the television station. However, for people who have lost a limb or become paralyzed, the inability to do these things means a loss of freedom and independence. This video segment from Greater Boston describes how neuroscientists and bioengineers have teamed up to create a system that allows people who have lost motor functions to control electronic devices through their thoughts alone. Grades 6-12

Why did sex evolve? The likely answers, in this essay for the Evolution Web site by science journalist Matt Ridley, may surprise you.

Recommended for: Grades 9-12