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.

Metals are grouped according to their characteristics. This video segment uses the periodic table for an in-depth discussion.

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.

This video segment from Nature explains the geologic forces behind the creation of HawaiiŒë_í_Œ_ dramatic shoreline.

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.

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.

Learn how a cow eats and digests food in this video segment from Nature.

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

In this video from Outdoor Nevada, learn about the habitat, diet, and defense mechanisms of horned lizards.

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

In this media-rich essay from the NOVA Web site, astronomer Brent Tully of the University of Hawaii walks you through the latest scientific theories about the size of the universe.

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.