AC / DC: What's the Difference?

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.

Acid Lake

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

Acids and Bases: Kitchen Chemistry

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

All in the Family

In this Evolution Web feature, test your skills at judging who's who on the tree of life while you learn about the tools and methods of cladistics.

Amplitude

This interactive activity adapted from the University of Utah's ASPIRE Lab shows how a pendulum's amplitude changes as you set it swinging from different distances from its axis, and how the amplitude of a sound wave changes as you adjust the volume.

Analyzing an Ecosystem

In this interactive activity adapted from the University of Alberta, identify the living and nonliving things in an ecosystem. Then look further at the living things to identify the producers, the consumers, and examples of mimicry.

Anatomy of a Rover

In this interactive activity from NOVA, learn about the sophisticated scientific instruments on two identical robotic rovers that have explored Mars — Spirit and Opportunity.

Anatomy of a Tsunami

Using visual models and other graphics, this interactive activity from NOVA Online reveals details of the December 26, 2004 tsunami that collided with coasts around the Indian Ocean.

Anatomy of a Volcano

In this interactive activity from NOVA Online, explore the main features of the Nyiragongo volcano, located in the Democratic Republic of Congo, and learn what risks it poses to the 500,000 people who live in its shadow.

Animal Classification Game

Learn about classes of animals and test your ability to identify animals as mammals, birds, reptiles and more in this interactive activity adapted from Sheppard Software.

Antarctic Ecosystem

In contrast with its largely lifeless interior, the Antarctic coastal marine environment supports a vibrant and diverse ecosystem. Explore the region's living bounty in this interactive activity adapted from the Woods Hole Oceanographic Institution.

Antarctic Food Web Game

In this interactive game adapted from the Bigelow Laboratory for Ocean Sciences, build a food web that illustrates the flow of energy in an Antarctic ecosystem and the relationships between predators and prey.

Arctic Atlas

In this interactive atlas adapted from UNEP/GRID-Arendal, explore different environmental features of the Arctic. Select from a list of themes to customize your map, then zoom in to take a closer look at one of six featured regions.

Arctic Ecosystem

Despite seemingly inhospitable conditions, the Arctic environment has a vibrant and diverse ecosystem. Explore the life that thrives in this region in this interactive activity adapted from the Woods Hole Oceanographic Institution.

Arctic Sea Ice Satellite Observations

In this interactive activity produced for Teachers' Domain, learn how Arctic sea ice has changed over the past 25 years in terms of maximum winter extent, concentration, and the timing of breakup each spring.

Astronomical Images in Different Wavelengths

Visible light is just one portion of the electromagnetic spectrum that a telescope may detect. This collection of images produced for Teachers' Domain features radio wave, infrared, visible light, and X-ray images of distant stars and galaxies as well as images of the telescopes designed to detect the various wavelengths of radiation.

Atmospheric Oxygen

In this feature, adapted from Interactive NOVA: "Earth," students explore the relationship between oxygen concentration and the well-being of various organisms by simulating a change in oxygen levels and observing what happens.

The Atom

In this interactive activity from ChemThink, take a closer look at atomic structure, properties, and behaviors.

Atom Builder

Build a carbon atom out of up quarks, down quarks, and electrons in this interactive activity from the NOVA Web site.

Bank It or Bust

In this interactive game from What's Up in Finance?, players make financial decisions to help them meet their goal of buying a car.

Bear Creek Wind Farm Tour

In this interactive, a construction project manager explains the process of constructing a wind farm, its challenges and benefits.

Biodiversity in the Dzangha-Sangha Rain Forest

In this interactive activity from the American Museum of Natural History, play "connect the dots" and discover the connections between the people, animals, and plants in three habitats of the Dzanga-Sangha rain forest in the Central African Republic.

Biomes

This interactive resource adapted from NASA describes the different temperature, precipitation, and vegetation patterns in seven biomes: coniferous forest, temperate deciduous forest, desert, grassland, rainforest, shrubland, and tundra.

Birth of a Supernova, Type Ia

In this interactive activity from NOVA Online, learn about a type of exploding star — a Type Ia supernova — that is so bright that astronomers can measure the distance to the galaxy in which it resides, and even learn which elements make up the star.

Birth of a Supernova, Type II

In this interactive activity from NOVA Online, learn about a type of exploding star — a Type II supernova — that is so large it has a mass 10 times greater than the mass of our Sun.

Blood Flow and Thermoregulation

In this interactive activity adapted from the University of Alberta, learn about the ways your body can regulate its temperature.

Body Breakdowns

This interactive feature from the NOVA "Surviving Denali" Web site details the variety of ways the body can fail while climbing a high-altitude peak.

Body Control Center

Throughout the day, your nervous system monitors and makes endless adjustments to your body's basic systems -- all to keep you alive. This interactive feature illustrates the complexity of such a task.

Body Needs

This interactive feature from the NOVA "Dying to Be Thin" Web site describes the nutritional needs of the body and how to meet them.

Bowhead Whaling and Its Impact

This interactive activity, adapted from material provided by the ECHO partners, explores the history of whaling in the Arctic and introduces a landmark study of whale populations.

Brain Geography

Which part of your brain controls your ability to swallow? Your instinct to survive? And how do all the brain's parts function cooperatively? Find out with this interactive feature from the NOVA: "Coma" Web site.

Build a Family Tree

Both sexes can use this interactive feature that lets you use DNA information from the Y chromosome to complete a male family tree. From the NOVA: "Lost Tribes of Israel" Web site.

Build an Island

This interactive resource from NOVA Online shows how an atoll is formed from a volcanic island and describes the role coral reefs play in this process.

Caves and Karst

This interactive resource adapted from the National Park Service presents the key concepts of cave and karst systems, including how and where they form, different types, and various cave environments.

Cell Membrane: Just Passing Through

This interactive feature describes some of the most important structures and functions of the cell membrane.

Cell Transcription and Translation

In this interactive activity adapted from the University of Nebraska, learn how and where transcription and translation occur within a cell and observe both processes in detail.

Center for Sustainability at Penn State University Tour

In this Flash interactive a guide to the Hybrid Homestead introduces the concept of ecological footprint or how big an impact humans make on the ecosystem. We visit a yurt, kitchen, bathroom, and greenhouse designed to reduce human energy needs.

Centripetal Force: Pulling Cs and Gs

In this interactive activity from NOVA, discover how centripetal force can affect you when riding in a car or flying at high speeds in a fighter jet.

Chemical Bonds

This interactive activity developed for Teachers' Domain demonstrates how attractive forces between atoms create chemical bonds, resulting in the formation of molecules and compounds.

Chromosome Viewer

This interactive feature provides a microscopic view of the 24 Human chromosomes. Each chromosome is labeled with the names of some of the genetic conditions and traits associated with particular regions on that chromosome.

The Civil Rights Movement in America, 1945-1975

This interactive timeline provides a chronological and geographic view of the events of the Civil Rights era and its aftermath.

Cloud Types

This interactive resource, adapted from NASA's S'COOL Project Tutorial, explains how you can classify and identify various types of clouds.

Coastal Geological Materials

This interactive resource adapted from the National Park Service describes the different kinds of sediments that make up coastlines, with a focus on the variety in color, size, and sorting.

Collisions on an Air Track

In this interactive activity adapted from the University of Toronto, observe the effect of mass on momentum in elastic and inelastic collisions.

Compare and Contrast Warm and Cold Fronts

This visualization from McDougal Littell/TERC visualizes the movement of warm and cold fronts and the cloud types that are generated as a result.

Compare the Poles

Explore the defining features of the Arctic and the Antarctic in this interactive activity adapted from the Woods Hole Oceanographic Institution.

Compost Office

This interactive activity from Keep America Beautiful, Inc. uses illustrated text and a game to explain why it is important to compost, the science involved, and the perfect recipe for decomposition.

Construct an Aqueduct

Think like an engineer and build an aqueduct in this interactive activity from the NOVA Web site.

Continental Divide: The Breakup of Pangaea

Examine geological evidence found in fossils, rock deposits, and ancient mountains that supports the theory of continental drift in this interactive activity adapted from the Exploratorium.

Cooking with Sugar

Find out about the chemistry of candy and how sugar reacts at different temperatures to become fudge, caramel, lollipops, and more in this interactive activity adapted from the Exploratorium.

Coral Reef Connections

Dive in and explore what makes this beautiful world so fragile. In this Evolution Web feature, discover how coevolution has shaped the ecological relationships among reef creatures.

Covalent Bonding

This interactive activity from ChemThink takes a closer look at a covalent bond—how it is formed and how the sharing of two electrons can keep atoms together.

Create a DNA Fingerprint

Learn DNA profiling, the technique police use to catch the guilty and free the innocent. From NOVA: "The Killer's Trail" Web site.

Creepy Crawlies

This interactive feature from the NOVA: "Odyssey of Life" Web site explores the often unwitting relationship we share with the billions of organisms that reside in our bodies and in our homes.

Crocodiles! Clickable Croc

This interactive feature from the NOVA "Crocodiles!" Web site details some of the characteristics that have enabled crocodiles to thrive for 200 million years.

Accessibility features: Long Description

Dance of Development

Watch the "dance" of development as a zebrafish egg divides and differentiates on its way to becoming an embryo in this interactive activity adapted from the Exploratorium.

Dances with Bees

This interactive feature from the NOVA "Tales from the Hive" Web site explores the methods honeybees use to communicate to their hivemates the location, quantity, and quality of nearby food sources.

Darwin's Diary

Delve into the private thoughts of a reluctant revolutionary in this Evolution Web feature.

De-Twinkling the Stars

Find out why stars twinkle and adjust a telescope to sharpen a star's image in this interactive activity adapted from NASA.

Deep Time

This interactive timeline from Evolution offers a visual representation of the major geological changes, transformations, and extinction episodes in the 4.6-billion-year history of Earth.

Deep Time

Explore 4 billion years of life on Earth and discover major transformations, geological changes, and extinction episodes in this Evolution Web feature.

Deforestation in Bolivia

This visualization adapted from NASA features two satellite images from 1984 and 2000 that show the dramatic deforestation of the Bolivian rainforest.

Design a Liquid Fuel Rocket Engine

Learn about rocket engines, and then design and launch a liquid fuel rocket in this interactive activity adapted from NASA.

Design an Ion Engine

Learn about ions and then design an ion engine to maximize thrust in this interactive activity adapted from NASA.

The Disappearing Aral Sea

This visualization adapted from NASA features satellite images showing how more than 60 percent of the Aral Sea has disappeared during the last 30 years.

Discovering Antarctica

Take a guided tour of Antarctica by watching brief video segments of its landscape and wildlife in this interactive activity adapted from the British Antarctic Survey.

Dissolving Salts in Water

In this interactive activity adapted from Iowa State University, design and carry out an experiment: dissolve salts in water, see how different ionic compounds produce different reactions, and observe the resulting changes in temperature.

DNA Workshop

How does DNA perform those all-important functions of replication and protein synthesis? This interactive feature from the A Science Odyssey Web site will help you explore and understand the secrets of DNA.

Documenting Glacial Change

This collection of comparative glacier images adapted from the National Snow and Ice Data Center shows substantial changes in five Alaskan glacier positions over periods of 60 to 100 years.

Dolly Garza: A Tlingit and Haida Scientist

In this interactive resource adapted from Raven Radio/KCAW, listen to biologist Dr. Dolly Garza as she explores the sea otter population of Sitka, Alaska, from the perspectives of her tribal heritage and her Western education.

Dust Explosion

In these videos adapted from the Journal of Chemical Education, observe how a material that is usually hard to ignite becomes very flammable when its particles are suspended in air.

Earth in Motion: Seasons

This interactive activity from the Adler Planetarium explains the "reasons for the seasons." Featured is a game in which Earth must be properly placed in its orbit in order to send Max, the host, to different parts of the world during particular seasons.

Earth’s Albedo and Global Warming

In this interactive activity adapted from NASA and the U.S. Geological Survey, learn about Earth's albedo (the ratio of reflected vs. incident solar radiation), how pollution alters albedo, and how ice-albedo feedback may accelerate global warming.

Electric Charges Interact

Experiment with electric charges to find out how they interact in this interactive activity adapted from NASA.

Energy Flow

This feature, adapted from Interactive NOVA: "Earth," follows the path of energy as it is transferred via the food chain from one type of organism to another.

Energy in a Roller Coaster Ride

See potential energy convert to kinetic energy in this interactive activity from WGBH that shows a roller coaster in action.

Engineer a Crop: Transgenic Manipulation

You're the geneticist now. In this interactive feature from the NOVA/FRONTLINE "Harvest of Fear" Web site, use the latest in genetic technology to engineer your own "supercrop" of tomatoes.

Everest: Test Your Brain

This interactive feature from the NOVA "Everest" Web site lets you take the same brain quizzes that researchers used to test the brain function of climbers on Mount Everest.

Evolution Revolution

From the Evolution Web site, explore the rise of a revolutionary idea and the controversies that surround it.

Examine Global Surface Currents

This visualization from McDougal Littell/TERC visualizes the relationship between global wind directions and the direction of ocean surface currents.

Explore a Stretch of Code

Try your hand at reading a segment of genetic code in this interactive feature from the NOVA "Cracking the Code of Life" Web site.

Explore the Moon

See what it is like to walk on the Moon by viewing this collection of QuickTime images from NOVA Online. Stunning 360-degree panoramas from each of the six successful Apollo Moon landings are featured.

Exploring the Arctic Seafloor

In this interactive activity adapted from NOVA scienceNOW, learn what some of the first imagery ever shot on the Arctic Ocean seabed tells us about life in extreme environments.

Exploring Tidepools

In this interactive activity adapted from the National Park Service, learn about tidepools and then try to identify the organisms that live there.

Forces Lab

In this interactive activity from the Building Big Web site, select one of the actions of squeezing, stretching, bending, sliding, or twisting to explore the forces of compression, tension, shear, and torsion.

Forecasting Volcanic Eruptions

This media-rich essay from NOVA Online describes the challenges of forecasting volcanic eruptions and includes information about specific cases.

Fossils: An Ancient Sea in Indiana

In this interactive activity from the Children's Museum of Indianapolis, Indiana, examine a piece of the ancient Borden Sea in what is now central Indiana. Explore the types of fossils found there and the clues they offer to ancient life on Earth.

Free-Falling and "Weightlessness"

Discover the difference between free-falling and weightlessness in this interactive activity from the NOVA Web site.

From Ridge to Reef: Adapting to a Changing Climate

Explore Pacific high island and atoll ecosystems, learn about the threats to island resources and residents, and discover how communities are preserving their future, in this interactive activity adapted from the Micronesia Conservation Trust.

Gallery of Auroras

View this stunning collection of auroral displays from NOVA Online to find out why auroras appear in different colors and shapes and whether they occur on other planets.

Gallery of Visual Illusions

Are your eyes playing tricks on you? Discover more about eyesight and the brain as you test your eyes with these visual illusions adapted from the University of Washington's Neuroscience for Kids Web site.

Gas Properties

In this interactive simulation adapted from University of Colorado’s Physics Education Technology project, change parameters and discover how the properties of a gas vary in relation to each other.

Gel Electrophoresis

This interactive activity from the Dolan DNA Learning Center illustrates the process of gel electrophoresis, in which DNA fragments are separated by size as they migrate at different rates through a gel matrix.

Genetics: Tour of the Basics

In this interactive activity from the University of Utah, identify different kinds of genetic traits and how they are passed on from generation to generation. View examples of simple and complex trait inheritance.

Giving Rise to the Jet Stream

This interactive activity from NOVA Online uses animation and graphics to offer a detailed explanation of the jet stream. A thorough account is given of the role played by the Sun's heat and Earth's shape and rotation, among other factors.

Glaciers

Featuring images of glacier formations, this interactive resource adapted from the National Park Service explains what glaciers are, where they are found, how they form, and how they move.

Global Trends Quiz

In this interactive quiz from NOVA, take the Environmental Challenge and test your knowledge of human impact on the world's natural resources and climate.

Global View of the Seasons

This interactive activity produced for Teachers' Domain features satellite data of Earth's seasonal cycles. Visualizations and comparative still images reveal how successfully plants are photosynthesizing at different times of the year.

Global Water Distribution

How much water on Earth is fresh water? How much of that fresh water is found in icecaps? Lakes? Rivers? This interactive resource uses bar graphs to illustrate the relative distribution of fresh and salt water on Earth. Adapted from Oxford University Press.

Graphing the Periodic Table

This interactive activity from the American Chemical Society presents the properties and electron configurations for all the elements in the periodic table. Discover patterns by plotting the elements' properties according to their place in the table.