Hands-On Activities

SciFri Pick of the Week

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Slime Time on Fox 2 News

Follow this recipe for a slimy good time! Thanks to Pallas Hupe and Fox 2 News for having us on Parent 2 Parent!

What you need

• Borax Powder
• White glue (Elmer’s)
• water
• 2 small bowls
• food coloring (optional)

What to do

1. In the first bowl, combine 6 teaspoons glue, 6 teaspoons water and the food coloring.
2. In the second bowl, pour ¼ cup water and ¼ teaspoon borax. Stir.
3. Slowly stir the glue mixture from the first bowl into the second bowl.
4. Once your slime has formed, pick it up and knead it i your hands.
5. There will be some liquid left in the bowl.
6. The more you play with the slime, the firmer it becomes.

What’s Happening?

When you mix the two together, the sodium tetraborate in the borax links all the chains of polyvinyl alcohol together into a rubbery, gooey mass. The water works like a bridge between the molecules and what do you have? SLIME!

Ice Cream in a Bag

What you need

• Gallon-size re-sealable plastic bags
• Small re-sealable plastic bags
• Ice (4 cups per person)
• 1 gallon whole (Vitamin D) milk
• 1 quart half and half
• Salt (¼ cup per person)
• Spoons
• 2 cups sugar
• 5 tablespoons vanilla

What to do

1. Create your ice cream mix by combining the milk, sugar, half and half and vanilla.
2. Place 4 cups of ice in a gallon size bag. Add ¼ cup of salt and shake the bag a little to mix it up.
3. Pour ½ cup of the ice cream mix into a small bag. Seal it tightly, getting as much air out as possible.
4. Place the small bag of ice cream mix in the large bag of ice and salt. Seal the outside bag.
5. Shake, shake, shake the bag for at least 5 minutes. You can wrap it in a towel if it gets too cold to handle.
6. When the ice cream is frozen, remove it from the outside bag and enjoy!

What’s happening?

By itself, melting ice has a temperature of 0°C (32°F). When heat flows into ice at that temperature (and heat always flows from a warmer place to a colder place), the ice doesn’t get hotter, it just transforms itself into water at that same temperature.

Salt lowers the freezing point of water from 0°C (32°F) to -30°C (-22°F). That’s why we can use it to melt ice on sidewalks and roads in winter. By putting salt on the ice, you encouraged the melting process so much that the ice began to use its own internal thermal energy to transform into water. The temperature of the ice dropped well below its usual 0°C and yet it kept melting. Eventually, the drop in temperature stops — but by then the mixture is about -10°C (14°F) or so. To melt more ice, more heat must flow into the mixture. When you put your bag of ice cream mix nearby, heat began to flow out of that bag and into the ice and salt water. More ice melts and the ice cream mix got even cooler. Eventually, the water and ice cream mix started to freeze. And what did you get? Ice cream!

Sound Science

What you need

• Cotton string
• Metal spoon
• Optional — metal cooling rack (the kind you use for cookies)

What to do

1. Tie a two-foot length of string to one end of a spoon.
2. Wrap the other end of the string around your finger a few times.
3. Gently swing the spoon so it hits a table top or other hard surface. What do you hear?
4. Press the string finger against your outer ear (do not stick your finger in your ear) and let the spoon swing into the table again. What do you hear this time?
5. If you have a cooling rack, tie two strings to it (one for each ear). Hold the strings to your ears and let the cooling rack swing into the table. What does it sound like now?

What’s happening?

Not only does the string (a solid) carry sound waves faster than air (a gas), but it directs them right into your ear. The sound traveling through the string is much louder because most of the sound energy is directed through the string only and not spread out into the surrounding air.