In this video segment adapted from NOVA, watch residents of the Peruvian Andes build a suspension bridge made entirely of grass. The ancient Inca were a textile society and thus skilled in working with natural fibers including alpaca and cotton. Still, it might surprise people today that their solution to crossing the canyons and gorges of their mountainous empire featured another fibrous material: grass. When you consider how they built a simple suspension bridge, you'll realize that not only was this a practical solution, it was also a safe one. In this video segment adapted from NOVA, watch residents of the Peruvian Andes as they build a traditional and functioning grass bridge the likes of which enabled the ancient Inca people to flourish for several hundred years. Grades 3-12.

This video segment, adapted from NOVA, traces the evolving history of theories about gravity and a force that may oppose it, along with our understanding of the impact of both of these forces on our expanding universe.

In this video segment from NOVA scienceNOW, learn about the effects of gravity as astrophysicist Neil deGrasse Tyson falls through a virtual hole through Earth's center.

In this video segment adapted from NOVA, a meteorologist explains how an unusual weather pattern led to one of the most devastating floods of this century.

Learn about a study in which participants discovered contaminants in their homes, and how green chemistry may provide alternatives to such everyday toxins, in this video adapted from Contaminated Without Consent.

This collection of six images captures the magnificence of human development -- the transformation from baby to woman.

This video segment explores how one marine biologist used the scientific process to discover how whales hear.

In this video adapted from Bullfrog Films, GwichŰ__Ű__ŒŒÇin Chief Evon Peter of Arctic Village, Alaska, describes his people's connection to the caribou and their passion to protect Alaska Native land and traditions.

Although repeatedly exposed to HIV, Steve Crohn's blood cells were never infected. Dr. David Ho investigates in this video segment from NOVA: "Surviving AIDS."

In this ZOOM video segment, join Hana as she learns traditional Japanese drumming with her Taiko group.

In this video segment adapted from United Tribes Technical College, meet Native Americans who are concerned about climate change and believe that action today can help future generations once again live in harmony with Earth.

Learn why heart disease, a largely preventable condition, is the leading cause of death in this country today, in this video adapted from The Hidden Epidemic: Heart Disease in America.

In this video adapted from the National Science Center, observe a demonstration to discover how helium gas is inert and hydrogen gas is reactive.

This video segment adapted from Interactive NOVA profiles two scientists who were surprised in 1984 to discover a hole in our atmosphere's ozone layer as big as the United States.

This video segment, adapted from NOVA, explores reasons why Homo sapiens had an advantage over Neanderthals in the pursuit of territory and natural resources.

This video segment is adapted from Building Big, a PBS series hosted by David Macaulay. It explores Hoover Dam's hydroelectric capabilities by explaining how it is able to harness the potential energy stored in the reservoir and convert it to electricity. It also discusses environmental impacts of the dam and others like it.

In this video segment from PEEP and the Big Wide World, children experiment with cardboard and build a house for their stuffed animals.

This narrated animation from Interactive NOVA: "The Secret of Life" illustrates DNA replication.

This video segment adapted from NOVA describes the emergence of life on the islands of Hawaii from a barren volcanic platform under the ocean waves to the rich explosion of life that covers the many climate zones of the islands today.

In this video segment adapted from NOVA, dramatic footage of avalanches and animations of ice crystals illustrate how a layer of weakly-bonded snow can contribute to a devastating avalanche.