“Hot!” I said, blowing up my cheeks. That’s about 175º F. So, really hot!
“Are you ready for this?” asked Dr. Caroline.
“Oh yes!” I shouted.
“So ready!” said Birdie.
Dr. Caroline asked us to stand a few steps behind her as she put her goggles firmly on her head. “So you girls are going to count to three backward for me.”
“Three. Two. One!” we cried.
And then Dr. Caroline poured the hot water into the bucket of nitrogen.
There was a loud crackly sound.
A cloud poofed into the air. It was so thick that I couldn’t even see my gloves.
“Oh, look look!” I shouted. “The liquid nitrogen turned into a gas. So cool!”
Ms. Gottfried tossed Dr. Caroline her phone so that she could start filming from behind the cloud. The crowd gasped and hooted and hollered.
“That was beautiful,” sighed Birdie. Kids and parents were out of their seats. The applause was super loud.
“Nice job on the countdown, girls!” said Dr. Caroline. “What kind of change was that?”
“A phase change!” I shouted.
“That’s right!” said Dr. Caroline. “The nitrogen molecules stayed the same, but the phase changed from liquid to gas.”
“Gas takes up more space than the liquid,” I said, looking up as the clouds of vapor started to disappear.
“Exactly,” said Dr. Caroline. “The molecules are more separated. And when they move from gas to liquid, the molecules go from far apart to close together.”
“Just like when farm dogs herd sheep,” added Birdie.
“That’s right! You guys are a great team,” said Dr. Caroline. She glanced at her phone. “Guess what?! We definitely raised enough money to fund every kid’s idea. And maybe a little to help out with the STEM Night next year.” She pumped her arm into the air.
Everyone cheered. Some people stomped on the floor with their feet.
“Science is awesome,” I said.
“You can say that again,” said Dr. Caroline.
“Science is awesome!” we all cheered.
Dr. Caroline shut down the fundraising app and put her phone in her lab coat pocket. “Thanks so much for having me here tonight, folks. Now go out and have more fun. There are tons of hands-on stations. Stay curious!”
Since science was involved—that definitely wouldn’t be a problem.
Lemon-Lime Clock
Materials:
3 lemons
3 limes
6 galvanized nails
6 pieces of copper wire (or 6 pre-1982 pennies)
7 alligator clips
1 digital clock
Pliers (if using wire instead of pennies)
Protocol:
If you’re using wire instead of pennies, use the pliers to cut 6 pieces of wire, each about 2 inches long.
Plunge 1 nail into the left side of the first lime [NAIL 1].
Plunge 1 copper wire (or penny) into the right side of the first lime [COPPER 1].
Plunge 1 nail into the left side of the first lemon [NAIL 2].
Plunge 1 copper wire (or penny) into the right side of the first lemon [COPPER 2].
Plunge 1 nail into the left side of the second lime [NAIL 3].
Plunge 1 copper wire (or penny) into the right side of the second lime [COPPER 3].
Plunge 1 nail into the left side of the second lemon [NAIL 4].
Plunge 1 copper wire (or penny) into the right side of the second lemon [COPPER 4].
Plunge 1 nail into the left side of the third lime [NAIL 5].
Plunge 1 copper wire (or penny) into the right side of the third lime [COPPER 5].
Plunge 1 nail into the left side of the third lemon [NAIL 6].
Plunge 1 copper wire (or penny) into the right side of the third lemon [COPPER 6].
Use one alligator clip to connect NAIL 1 and COPPER 2.
Use one alligator clip to connect NAIL 2 and COPPER 3.
Use one alligator clip to connect NAIL 3 and COPPER 4.
Use one alligator clip to connect NAIL 4 and COPPER 5.
Use one alligator clip to connect NAIL 5 and COPPER 6.
Remove the battery cover and the battery to expose the positive/negative side of the clock.
Use another alligator clip to connect NAIL 6 to the negative side of the clock.
Use the last alligator clip to connect COPPER 1 to the positive side of the clock.
Enjoy your Lemon-Lime Clock!
How It Works:
Our lemons and limes form a battery that is strong enough to power a small digital clock. For it to work properly, the negative terminal on the clock must be connected to the nail, and the positive terminal must be connected to the copper wire. The electrons travel from the zinc through the lemon/lime to the copper electrode. From here, they move through the wire to the neighboring zinc electrode to repeat this process. The electrons eventually leave the last lemon/lime through the wire to the digital clock. What happens when you reverse the alligator clips? This action stops the natural flow of electrons from high energy to low energy. Batteries work as a result of the spontaneous travel of electrons from metal to metal; the electrons cannot flow in the opposite direction unless they have an external power source (like a battery). Can you imagine plugging your lemons and limes into the wall to recharge them?
Dr. Kate Biberdorf, also known as Kate the Chemist by her fans, is a science professor at UT–Austin by day and a science superhero by night (well, she does that by day, too). Kate travels the country building a STEM army of kids who love science as much as she does. You can often find her breathing fire or making slime—always in her lab coat and goggles.
You can visit Kate on Instagram and Facebook @KatetheChemist, on Twitter @K8theChemist, and online at KatetheChemist.com.
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The STEM Night Disaster Page 8
