Family Science
Hovercraft
Imagine zooming across San Diego Bay in a boat that seems to float several inches above the water’s surface. Although this might sound like a scene from a futuristic science fiction film, hovercraft have been around for more than 50 years. These versatile vehicles are used by the military, search and rescue teams, wildlife biologists and scuba divers.
The first modern hovercraft was invented in the 1950s by Sir Christopher Cockerell. After testing his ideas using an empty cat food can, a coffee can and an air blower, he built a working model out of balsa wood. Today, most hovercraft are powered by large fans. These fans force air under the craft, where it is trapped by a skirt made of rubber or fabric. Additional fans blow air out of the back of the hovercraft, causing it to move forward. Because hovercraft can float on a pocket of air, they are able to travel over many different surfaces, including water, snow and sand.
Since August is National Inventors Month, it is the perfect time to take a closer look at these crazy contraptions. Put on your thinking cap and follow the directions below to see if you can improve on the basic hovercraft design.
Materials:
CD
Large balloon
Empty thread spool
Hot glue gun
Caution: Adult supervision is required for this activity.
To Do:
1.) Use the hot glue gun to glue the spool to the center of the CD. Be sure the hole in the bottom of the spool lines up with the hole in the CD.
2.) Let the glue dry for several minutes.
3.) Inflate the balloon and twist the neck so that no air escapes.
4.) Without untwisting the balloon, carefully stretch the open end over the top of the spool.
5.) Set your hovercraft on a clean, smooth surface, such as a kitchen table.
6.) Untwist the balloon and give your CD a slight flick with your finger. Watch your hovercraft glide across the table!
Now Try This:
Can you design a hovercraft that hovers longer or travels farther? Try using different sizes of balloons. Do some balloons work better than others? Build another hovercraft using a small plastic plate or a thin piece of cardboard in place of the CD. Which hovercraft works the best?
What’s Going On?
If you try to push your hovercraft across the table when the balloon is deflated, you will notice that it does not travel very far. The CD and the table rub against one another, creating friction. This friction causes the craft to slow down and stop. When you inflate the balloon and let it go, the air flows out of the balloon and goes under the CD. This layer of air reduces the friction because it keeps the CD from rubbing against the table. When there is less friction, your hovercraft travels faster and farther.
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Debbie De Roma is the education manager at the Reuben H. Fleet Science Center.
Candy Chromatography
June is National Candy Month. While this might sound like an excuse to eat a bunch of lollipops or chocolate bars, there are other ways to celebrate. For instance, many science experiments involve candy. Follow the directions below to find out how you can use science to determine how candies get their colors.
Materials:
Coffee filters
Clear jars or cups
Pencil
Tape
Scissors
Measuring cup or pitcher filled with water
Colored candies (M&Ms, Skittles, or Reese’s Pieces work well)
To Do:
1.) Cut the coffee filters into several strips. Each strip should be about 1” wide and just slightly longer than the height of your cup or jar.
2.) Fill one cup with a small amount of water.
3.) Choose one of the brown or purple candies.
4.) Dampen the candy by briefly dipping it in the water.
5.) Shake off any excess water and then smudge the candy on one of the filter strips, approximately 1” from the bottom.
6.) Fold the opposite end of the filter over a pencil and secure it with a piece of tape.
7.) Lay the pencil across the top of a second cup so that the strip hangs down inside the cup.
8.) Use a pitcher to carefully add enough water to the cup so that the water just touches the bottom of the filter strip. The water should not touch the candy smudge.
9.) Now watch closely as the water begins to travel up the filter paper. What do you notice? What happens when the water reaches the candy smudge? Keep watching for several minutes. Do you see any other colors on the filter?
10.) When the water reaches the top of the filter paper, remove it from the water and set it aside to dry.
11.) Repeat steps three through nine with some of the other candies.
Now Try This:
Repeat the investigation with different types of candies. Do you get the same result? What might happen if you dissolved a small amount of salt in the water? Try it and find out.
What’s Going On?
Look closely at the list of ingredients on a bag of M&Ms or Skittles. In addition to traditional ingredients, like chocolate and sugar, you may notice Red 40 or Yellow 6. These are the dyes that give the candies their colors. By using a process called chromatography, you can determine which dyes were used to make the different candies.
Chromatography is a method for separating mixtures, such as candy dyes, into individual parts. In this case, the separation is accomplished by using a coffee filter and water. As the water travels up the filter, it carries the dyes along with it. Different colors of dye travel at different rates due to their size, their solubility, and their attraction to the filter paper. The color molecules that are the most soluble in water or that have the least attraction to the paper travel up the paper the fastest. Those color molecules that have less solubility or that are more attracted to the paper travel more slowly.
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Debbie DeRoma is the Education Manager at the Reuben H. Fleet Science Center.
Egg-ceptional Science
With the Easter Bunny scheduled to make his deliveries this month, there is a good chance you have a few extra eggs in the refrigerator. If you get tired of eating all these eggs, you can save a few for science experiments. Be warned—this investigation takes a few days. You will need a little patience, but it’s definitely worth the wait.
Materials:
Raw egg
Clear jar or cup
Vinegar
Refrigerator
To Do:
1.) Place the egg in the cup and cover it with vinegar.
2.) Look closely at the surface of the egg. What do you notice? You may see bubbles forming on the outside of the shell.
3.)Place the cup with the egg in the refrigerator for 24 hours.
4.)On the second day, carefully pour the vinegar into the sink.
5.) Now, cover the egg with fresh vinegar and return the cup to the refrigerator.
6.) Leave the cup in the refrigerator for another six to seven days. You can check on the egg periodically, but don’t disturb it too much. Be sure to pay attention to the bubbles coming off of the egg.
7.) After a week, remove the cup from the refrigerator and carefully pour off the vinegar.
8.) Gently lift the egg out of the cup and rinse it with water. What do you notice? What happened to the shell?
Now Try This:
Repeat the investigation with a hardboiled egg. What do you notice about the texture of the egg after it sits in vinegar for a few days? Would you get the same result if you used another type of liquid such as lemon juice or soda? Try it and find out!
What’s Going On?
The egg’s shell is made of calcium carbonate. This is what makes the shell hard and gives it its strength. Vinegar is actually a type of acid, called acetic acid. The vinegar reacts with the eggshell, causing the shell to break down. This chemical reaction produces the carbon dioxide gas bubbles that you see on the surface of the egg. Once the shell is completely gone, the only thing that remains is the delicate membrane of the egg. Some of the vinegar actually enters this membrane, making the egg a bit bigger. If you try this investigation with a hard-boiled egg, you will notice that the egg feels very rubbery.
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Debbie DeRoma is the Education Manager at the Reuben H. Fleet Science Center.