This video segment adapted from NOVA shows how scientists use the fossil record to trace when early human ancestors and related species began walking on two legs instead of four, and to determine whether they were more apelike or human in appearance.

Learn how to make waves of all different shapes by adding up sines or cosines. Make waves in space and time and measure their wavelengths and periods. See how changing the amplitudes of different harmonics changes the waves. Compare different mathematical expressions for your waves.

In this interactive activity adapted from the University of Utah's ASPIRE Lab, investigate frequency in terms of trampoline jumps, pendulum swings, and electromagnetic waves.

Watching plants grow is like watching paint dry: It happens so slowly that the changes are imperceptible from one moment to the next -- and yet the end results are dramatic. This video segment shows just how amazing plant development can be by depicting various phases of the process using time-lapse photography. Footage from NOVA: "The Shape of Things."

In this video excerpt from NOVA, find out how the discovery of a gene defect has led to the development of a new drug to treat patients with cystic fibrosis.

This video segment describes the basics of the circulatory system: how the heart pumps the blood that carries oxygen and nutrients throughout the body.

This video segment adapted from NOVA scienceNOW shows how the common wood frog freezes solid every winter, an adaptation that allows the organism to survive the cold winter.

In this video segment adapted from NOVA scienceNOW, hydrogen fuel cell cars promise pollution-free driving, but will we see them anytime soon?

In this video segment adapted from FETCH!, contestants are challenged to use materials from a garbage dump to build a boat that floats, can be steered, and is propelled by something other than oars.

Just after World War II, nuclear scientists turned their attention from fission to fusion. This video segment adapted from AMERICAN EXPERIENCE looks at the beginnings of thermonuclear power generation.

This video segment adapted from NOVA shows how Galileo, using his newly developed refracting telescope, observed four of Jupiter's moons, the first astronomical bodies to be discovered since ancient times.

Einstein called Galileo the "father of modern physics." This media-rich essay from the NOVA Web site looks at Galileo's quest to understand the mathematics of motion.

In the early 1600s, most people believed that the Sun revolved around a stationary Earth. This video segment adapted from NOVA tells how Galileo proved that the Sun, not Earth, is at the center of our universe.

This video segment adapted from NOVA shows how Galileo used his telescope to carefully observe and study sunspots.

Scientists don't always get it right. This video segment adapted from NOVA looks at Galileo's failed theory for the motion of the tides.

This video from NASA describes the GLAST satellite, which is equipped with a gamma-ray telescope, and shares some background about the kinds of extreme universal phenomena indicated by the presence of gamma rays.

This video segment from Swift: Eyes through Time introduces and explains theories of the origin of gamma-ray bursts.

This video segment from the Secret of Life School Video: "On the Brink: Portraits of Modern Science" explores the genetics of breast cancer.

The shared set of genes for body segments, possessed by all animals, are discussed in this video segment from Evolution: "Great Transformations."