Perhaps you don't have enough class periods to do every science experiment you wish you could, or maybe your budget for beakers and baking soda is all tapped out. Maybe you just want to watch and see how it's done before you try to build a volcano with 24 fourth-graders. Whatever the reason, having students watch a science demonstration close up on the Web is the next best thing! Read on to discover 40 favorites for K-8 students chosen by the great people at the X-Ray Vision-aries blog. They may even inspire your students' next science fair projects!

1. Dry Ice Bubble

This fun, simple demonstration of how to create a giant soap bubble with dry ice will have your students' eyes popping.

2. Glow Sticks-Liquid

Light Kids love glow sticks. Ask them how they work and the likely answer will be "batteries." The answer is simple science. This cool experiment on the luminescent science behind glow sticks is one of many fantastic and informative videos on YouTube hosted by Steve Spangler.

3. Inertia Experiment

This basic experiment using a pen cap, a bottle, and a crochet hoop demonstrates one of Sir Isaac Newton's most fundamental principles — "an object at rest stays at rest."

4. How to Make a Rain Cloud in a Bottle

Teach kids the curious process of condensation with a bicycle pump, a soda bottle, and a few other simple items. This is a great way to teach the science behind everyday weather.

5. Afraid of Pop Rocks?

Discovery Channel's venerable Mythbusters team uses science to debunk the popular urban legend that the combination of Pop Rocks and soda could cause your stomach to explode. Use this video to talk with your class about how to pose scientific questions.

6. How Do You Keep an Egg From Breaking?

How Stuff Works creator Marshall Brain offers a kid-friendly look at the science behind a shattering egg. How can you drop an egg from a height of two feet and not have it break? Watch this video with your students and invite them to figure it out!

7. Surface Tension

Science Bob shows you how to make a paperclip (and a coin!) float on water with a little bit of dish soap.

8. CO 2 is Heavier Than Air

Using household ingredients, this experiment illustrates the weight of carbon dioxide when compared with other gases in the atmosphere. This is an ideal experiment for introducing your students to the concept of greenhouse gases and global warming.

9. Where Do Ocean Currents Come From?

Without motion in the ocean, there wouldn't be nearly as many different things living in the sea. Teach your students how the ocean ebbs and flows and the behavior of different types of currents with Bill Nye's informative, detailed demonstration.

10. How Much Sugar Is in a Can of Soda?

This great kitchen science experiment dealing with nutritional values and evaporation will have your students thinking twice before the next time they ask for a glass of their favorite drink. The shocking answer? In every 12-ounce can of soda, there is about seven and 1/2 teaspoons of sugar.

11. The Science Behind the Olympics

Steven Spangler demonstrates how air flow and resistance affect the speed and performance of a ball in the air or a relay runner on the track. Students who love sports will find themselves fascinated by the forces at work in their favorite games.

12. Why Won't This Balloon Pop?

This video will appeal to kids and adults alike, showcasing an enjoyable experiment involving a seemingly invincible balloon.

13. Harry Potter: Three Magical Experiments

Sometimes science can look a lot like magic. In this video, scientist Dan Jambuck shows kids step by step how to make a fizzy potion and invisible ink with kitchen ingredients. Do these with your students and have them record their scientific observations in invisible ink!

14. How to Build a Water Rocket

One of the many delightful videos hosted by eHow's Expert Village involves instructions on building a water rocket out of a plastic bottle, demonstrating how air pressure works. The step-by-step instructions are easy to follow or to duplicate in your own classroom.

15. The Tea Bag Rocket

Simple, fun, quirky, and entirely feasible for the classroom, the tea bag rocket looks at science from an unexpected angle. Use this quick video lesson to teach your students about the density of air and how it is affected by changes in temperature.

16. How to Make a Miniature Volcano

Some teachers see the vinegar and baking soda volcano as something of a science fair clichÃ©. It may be an oldie, but it's a still a goodie. Watch this with your students before creating your own mini Krakatoas.

17. Exploding Piñatas

Watch seventh- and eighth-graders design a piñata that explodes on its own and sprays the room with candy. A good model of the scientific process-students come up with the goals of their experiments and test several models to determine success.

18. The Science of Solids, Liquids, and Gases

Using ingredients readily available at grocery, drug, and hardware stores, children can learn about the properties of matter.

19. How to Make a CO 2 Sandwich

Here's a fun activity that uses some common items that you'll find around the house and a little creativity to explore the "pop" factor of vinegar and baking soda. Steve Spangler and his second-grade assistants create "sandwich bombs" out of plastic bags and simple chemistry.

20. How Does Your Body Digest Food?

In this video, Marshall Brain dives into the digestive process and presents an experiment that replicates how the stomach and large and small intestines break down food.

21. Exploding Bubbles

What happens when heat is applied to bubbles created using hydrogen gas? The video experiment starts slow but ends with a bang.

22. Hair-Raising Science

Get students charged up for a lesson on static electricity. Bill Nye uses a van de Graaff generator to explain how electrical charges attract and repel.

23. How to Make a Glacier Out of GAK

Elmer's glue, Borax, and a few other ingredients are used to demonstrate the properties of an arctic glacier. Both GAK and glaciers are polymers that can stretch or break depending on the amount of pressure applied. If there is a lot of pressure on a glacier, ice will crack or break (causing crevasses in glaciers); when the pressure is lower or the strain rate is small and constant, ice can bend.

24. The Electric Pickle

Another super demonstration from Steve Spangler, this amusing and highly informative experiment uses a pickle in a simple electric circuit. Your students will light up when the pickle turns red and glows! A great introduction to the science of electricity.

25. How to Make a Tornado in a Bottle

With simple ingredients, students can create a miniature whirlpool that illustrates the movement and behavior of water with artistic flair.

26. Acid Base Indicator

How can a cabbage help determine whether a solution is acidic or basic? BeardedScienceGuy demonstrates how to create a simple, colorful indicator that students can use to design their own acid base chemistry experiments.

27. Why Does Ivory Soap Float?

This simple experiment shows students the secrets behind Ivory Soap's unique physical structure that allows it to float.

28. How to Make Flubber

Slime and other gooey substances are an undeniable favorite when it comes to kid-friendly science experiments. Follow the step-by-step instructions to make it in your own classroom.

29. The Sticky Note Experiments

This smart, funny video will teach you and your students how to make a "waterfall" out of sticky notes. The video is entirely without words and only about a minute long, but it will inspire your students to want to make their own experiment videos. (Tip: Share the videos at your next science fair.)

30. Walking Water Rainbow

Students will love this science experiment done by kids, for kids. 11-year-old Aiden demonstrates color-mixing and absorption as he creates a rainbow using easy-to-find materials from around the house.

31. How to Build a Catapult

One of the most basic physics projects around is also one of the most enjoyable. Colin Kilbane teaches viewers how to make a tiny, very simple machine. Building a catapult is simple: Use a block of wood as a base, a plastic spoon as the arm, and two push pins and a rubber band as the torsion energy. What's your ammunition? Mini marshmallows, of course.

32. Light Bends and Bounces

The science videos of Bill Nye the Science Guy are produced by Disney and couldn't be clearer or more appealing to students. Do your students know why light bends through a lens? Bill shows us why. Notice that the light changes direction every time it goes from air to plastic, and then again when it goes from plastic to air. It slows down and speeds up. When that happens, it just can't help but bend.

33. What Happens When You Mix Diet Coke and Mentos?

The scientists test their theories on why soda turns into a fountain if you drop in a Mento. Show this to students after trying the experiment and challenge them to propose their own theories.

34. How to Walk on Water

This extremely messy experiment is an argument in itself for using video in your classroom. A mixture of cornstarch and water teaches kids about non-Newtonian fluids while at the same time shows them how to walk on it without sinking.

35. What is Energy?

Bill Nye introduces the concept of energy with his kinetic style, a bowling ball, a piece of glass, and a barbecue. Energy can change from one form to another. Watch as it makes things go, run, and happen.

36. Are Elephants Afraid of Mice?

The Mythbusters investigate the truth behind the old tale of whether mighty pachyderms are afraid of tiny rodents. The results might surprise you!

37. How to Make Butter

Show your students this video hosted by the always pleasant Robert Krampf before having them make their own butter from soured cream.

38. Feel the Pressure

Pressure pushes in all directions at once. Bill Nye goes scuba diving and journeys to the Hoover Dam with a jackhammer to demonstrate the concept of underwater pressure.

39. The Egg and the Bottle

Steve Spangler offers up a new perspective on the tried-and-true classic experiments in which a hard-boiled egg pops into a bottle when the bottle is heated. Why does it work? When molecules of air heat up, they move far away from each other and take up more space.

40. Bowling and Momentum

To explain the concept of momentum, Bill Nye shows the universal forces at work in the difference between throwing a ping-pong ball and a bowling ball at the pins.

How to Choose a Science Fair Topic

Help your students choose topics that will bring out their best work. The hardest part about doing a science project is picking the right experiment. Sure, you can look at websites that list ideas that have already been done. But the best projects come from children's everyday questions and observations about the world around them.

An experiment can be as simple as "Why do I feel hotter when I wear the red side of my jersey instead of the white when I play soccer?" or "Do I really need to go to bed at 8:15 every night?" When kids look around and ask questions about their lives, they can make the most rewarding projects.

To start, ask them when was the last time they wondered why something happened or how something worked? Suggest they think about their favorite hobbies (skateboarding, cooking, video games) and ask "why does..." questions about the hobby.

Look at television commercials and question their claims.

Ask open-ended questions such as, "What is the effect of x on y?" "How does x move?" or "How does y react when you blow on it?"