For any of these experiments, it's a good idea for an adult to supervise children, to always wear safety glasses, and if working with fire, to have a fire extinguisher handy.
Amaze Your Friends With a Fireproof Balloon
For this experiment, all you need is a balloon and a candle. Fill the balloon three-quarters full with water, and top it off with air by blowing the balloon up as far as it will go. Tie it off.
Light the candle, then slowly lower the balloon over it. Behold, the balloon won't pop!
This is due to water's incredible ability to absorb heat. The water in the balloon disperses the heat generated by the candle, and keeps the latex of the balloon from getting hot enough to break. But, when the water in the balloon can't absorb any more heat from the candle, the balloon will burst, and you'll probably get a little wet.
The Lava Lamp
From your kitchen, grab a bottle of vegetable oil, food coloring, some salt, and either a large glass or a glass jar.
Fill the glass container 2/3rds full of water and fill the remainder with vegetable oil. Add some food coloring, then slowly pour one teaspoon of salt into the container. Watch as beautiful colored orbs of oil gently fall to the bottom of the container.
At first, the oil will stay at the top of the container because oil is lighter than water. The key to making the oil fall to the bottom is the salt, it binds to the oil, making it heavier than the water. However, once the salt dissolves in the water, the oil will rise again to the top of the container. Groovy!
Grow Some Crystals
This classic experiment takes few days to complete, but it's well worth the wait.
You'll need some distilled water, salt or Epsom salts, a piece of wire or a pipe cleaner, and a glass container. First, heat the distilled water to a point just below boiling. Fill the glass container at least half full with the hot water. Add enough salt or Epsom salts to the water to create a saturated solution (the point when no more salt will dissolve in the water) and stir well.
Make a loop in the wire or pipe cleaner and lower the wire into the mixture. Place the container in a warm spot and wait. After a few days, you should see spectacular crystals forming on the loop of the wire.
This experiment works because of the temperature change of the water, and the solubility, the capability of the salt to be dissolved. As the water cools, the solubility of the solution decreases, and the salt precipitates out of the solution and onto the wire to form crystals.
Build a Popsicle Stick Catapult
To build this mini-catapult, you'll need at least 10 large popsicle sticks, a bunch of rubber bands, a pair of scissors, and some marshmallows for cannonballs. Marshmallows for cannonballs? How dastardly!
Stack eight popsicle sticks, and hold them together with rubber bands at each end. On the two remaining sticks, use the scissors to make a small notch on each side of the stick. Place them together and use a rubber band to hold the sticks together at the notch.
Then, pull the two sticks slightly apart and slide the eight-stick bundle between them. Steady your new catapult with one hand, and use your other hand to place a marshmallow on the top stick. Pull it back and release to fire!
You can also bind a plastic spoon with a rubber band to the top stick to make a bucket for holding your cannonballs. The castle walls will fall!
Make a Prism
You can make a rudimentary prism with just distilled water and clear gelatin. Empty a packet of gelatin into a pot and add only half the amount of water listed in the gelatin package instructions.
Place the pot on the stove, and as the pot warms, stir the gelatin gently to dissolve it. After the gelatin has dissolved, place the mixture into a small container and let it sit for 30 minutes to cool.
Cut the gelatin into squares or prism shapes, which is half of a square or rectangle cut on the diagonal. Shine a flashlight through the gelatin to see the light broken up into its spectral colors. You can also shine a laser pointer through the gelatin to see the light bend.
Create a Whirlpool
You can make a cool whirlpool by using two empty 2-liter soda bottles, a metal washer that has an opening smaller than the mouths of the bottles, and duct tape. Fill one of the 2-liter bottles, 2/3 full of water.
Place the washer on top of the filled bottle, and place the empty bottle upside down on top of the washer. Tape the two bottles together and quickly flip the bottles. You should see a water vortex (aka whirlpool) form as the water from the top bottle flows into the bottom bottle.
The vortex forms because the water spins faster around the edges of the bottle, creating a hole in the middle. This vacuum then fills with air from the bottom bottle, and water from the top bottle flows around it.
Build a Potato Battery
For this experiment, you'll need a potato, a galvanized nail, a piece of copper sheeting, or a copper coin such as a penny, two alligator clip leads with clips on both ends, and a voltmeter.
Galvanized nails have a zinc coating, and they can be purchased at any hardware or home improvement store. Be sure to use a fresh potato because the experiment depends on the liquid inside the potato.
Stick the galvanized nail into the potato, making sure that it doesn't go all the way through. About an inch (2.5 cm) away from the nail, stick in the penny.
Connect the penny to the red lead of the voltmeter using one of the alligator clips. Most voltmeters have red and black leads, but if your voltmeter has yellow and black leads, connect the penny to the yellow lead.
Connect the galvanized nail to the black lead of the voltmeter, and make sure both alligator clips are securely attached. Your voltmeter should show a positive reading. If it shows a negative value, simply switch the leads. You've produced electricity from a potato!
Construct a Balloon Hovercraft
You can make a small hovercraft that can slide along floors and tables by putting friction and Newton's Third Law of Motion into action. You'll need a balloon, the cap from a one or two-liter plastic soda bottle, a CD or DVD that you no longer use, an etching knife or scissors, and a glue gun.
First, create a nozzle by using the etching knife or scissors to create a hole in the bottle cap about the width of a drinking straw. Place glue all around the rim of the bottle cap, and attach it to the center of the CD or DVD. Wait for the glue to dry then check to see if has made a good seal with the CD or DVD, reapply glue if needed.
Blow up the balloon and pinch off the opening with your fingers then wrap the opening of the balloon around the nozzle of your hovercraft. Place the hovercraft on a flat surface and watch it go!
The Egg in a Bottle
This "oldie but goodie" experiment shows the relationship between atmospheric pressure and temperature. You'll need a couple of boiled and peeled eggs and a glass bottle or jar that has an opening that is somewhat smaller than the diameter of the boiled eggs. You'll also need a small piece of paper and a source of fire, such as a match or lighter. Parents should help kids with this one.
Place the glass container on a table and fold the paper into a strip that will fit inside the glass container. Light one end of the paper strip and drop the burning paper into the container. Next, set the egg on top of the opening of the glass container, and wait.
As if by magic, the egg will be sucked slowly into the bottle. This happens because the burning paper has changed the air pressure within the bottle. Soon after the egg is placed on top of the container, the fire will be extinguished, and the air inside the container will start to cool and contract. This lowers the air pressure within the container, so that the pressure in the container is lower than the air pressure outside the container. Because air flows from a high-pressure system to a low-pressure system, the higher outside pressure pushes the egg into the bottle.
You can do all these experiments at home with kids, and they are a wonderful introduction into the worlds of science and engineering.