Gak is a non-Newtonian fluid. In their natural state, glue molecules stick to each other only weakly, which is why glue flows smoothly and why it's easy to smear flat when you're using it to stick two other things together.
Much like the cornstarch used to make oobleck, glue molecules are long and slippery. Unlike oobleck, making gak involves a chemical change and the two ingredients cannot be separated out again.
We made the gak by adding boron atoms (in a water solution) to glue. These atoms crosslink with the sulfur atoms in the glue molecules, causing them to tangle and knot together. This happens immediately, with the glue wrinkling up as soon as boron is added and then forming into ropy webs when it's stirred.
The result is a substance that sticks to itself more than everything else. In fact, gak does so strongly enough that after I made the demo batch, I could clean my hands off by pressing the main ball of gak on my hands so it pulled in the errant bits.
The kids experimented with the gak for a while. Gak bounces like rubber. It rips when pulled quickly but can stretch to amazing lengths if the same is done more slowly. It's also completely non-toxic, so it's safe to eat (although I wouldn't recommend it with how often it fell on the floor). Pressed against interesting textures, it can be pulled off again to show the pattern.
If you do find gak stuck on fabric, vinegar reverses the reaction, breaking the gak back into boron and glue molecules that can be wiped off.
The standard slime gak is more liquid than the version we made. It's fun because it flows more easily but is more of a cleanup concern because it flows more easily into things like cloth and carpet, where it has to be washed out.
If you'd like to try making the slimier version of gak at home, it can be done by mixing equal parts glue and water (most recipies suggest one 8 ounce bottle of glue) and then adding dissolved borax - you can find borax in the laundry aisle as a powder. Add a teaspoon of that powder to a half cup of warm water, stir it up, and add the liquid to the glue. It should turn ropy on contact and tighten up as it's stirred until it's an semi-firm blob, at which point it can be squeezed and pounded into even consistency.
When we finished with the gak and discussing its properies, we moved on to our next unit, physics! We focused g-forces, which produce gravity-like effects. This is what allows people to spin a bucket full of water over their head without any of it falling out. It can also be felt by spinning around with your arms out, being spun around by someone else until you lift off the ground, or spinning in a chair and trying to keep your legs in. While it's mostly fun for fooling around here on Earth, it could be used to simulate gravity and allow humans to live in space indefinitely and even have children born and raised in space safely.
If your kids would like to try it at home, here's a more extensive demonstration video that also gets into Newton's Laws of Motion, which we'll go through in the next class.
Also, here's a video of a bullet fired into a water balloon!
Can your kid figure out what happened? We'll be discussing this and other aspects of physics next class.
Wednesday, January 15, 2014
Tuesday, January 7, 2014
Atoms, Molecules, Mixtures and Compounds
Hi everyone and welcome back!
Today we started off with a refresher about atoms and molecules. Individual atoms combined into larger molecules can display very different traits. To illustrate this, we made glucose molecules, which are composed of hydrogen, oxygen, and carbon. Despite being made of life-giving oxygen, you can't breathe it, just like you can't breath water despite it containing oxygen. And glucose molecules are the component parts of starches, which taste extremely bland.
Starch is a good source of energy, however, because it can be turned into sugar. In our mouths, we produce enzymes in our saliva that begin to break it apart into those sugars, so that if you hold something starchy in your mouth, it will begin to taste sweeter. It's believed this adaptation helped our ancestors know to eat starchy foods. We tried it out with corn starch and, although it's not very sweet compared to modern day candies we make out of pure sugar, it's still possible to taste the change.
Then we made oobleck by adding water to the cornstarch. Oobleck does not form a new molecule when the two ingredients are combined and can actually be separated very easily - simply squeezing it hard enough, as the kids tried, will push the water out again and turn it into damp corn starch. The resulting substance does have some very unusual properties, though, due to its ability to shift rapidly between solid and liquid depending on pressure. My favorite is that you can cause the fluid to tear if you try to make ripples the way you would in water.
If your kids want more time to play with it, it's very easy to make at home. Just pour some cornstarch into a bowl and add a bit of water until it has the right consistency - your kids should be able to tell you when it's right!
Next week, we'll talk about exactly why oobleck has these properties and then make gak, a compound.
Today we started off with a refresher about atoms and molecules. Individual atoms combined into larger molecules can display very different traits. To illustrate this, we made glucose molecules, which are composed of hydrogen, oxygen, and carbon. Despite being made of life-giving oxygen, you can't breathe it, just like you can't breath water despite it containing oxygen. And glucose molecules are the component parts of starches, which taste extremely bland.
Starch is a good source of energy, however, because it can be turned into sugar. In our mouths, we produce enzymes in our saliva that begin to break it apart into those sugars, so that if you hold something starchy in your mouth, it will begin to taste sweeter. It's believed this adaptation helped our ancestors know to eat starchy foods. We tried it out with corn starch and, although it's not very sweet compared to modern day candies we make out of pure sugar, it's still possible to taste the change.
Then we made oobleck by adding water to the cornstarch. Oobleck does not form a new molecule when the two ingredients are combined and can actually be separated very easily - simply squeezing it hard enough, as the kids tried, will push the water out again and turn it into damp corn starch. The resulting substance does have some very unusual properties, though, due to its ability to shift rapidly between solid and liquid depending on pressure. My favorite is that you can cause the fluid to tear if you try to make ripples the way you would in water.
If your kids want more time to play with it, it's very easy to make at home. Just pour some cornstarch into a bowl and add a bit of water until it has the right consistency - your kids should be able to tell you when it's right!
Next week, we'll talk about exactly why oobleck has these properties and then make gak, a compound.
Tuesday, December 10, 2013
Matter and mass
Today we entered into the realm of chemistry! We began about matter, atoms, mass and weight, using snow as an example substance because it shifts very easily between the three states of matter: solid snow, liquid water, and gaseous vapor. To demonstrate this, we heated snow to melting, then boiled the resulting water, and I held a metal sheet containing more snow above it to show how the vapor turned back into beads of liquid water when the cold metal sheet reduced its temperature.
We also discussed how if they were on the moon or one of the other planets their weight will be different because the gravity is different, which is based on the planet's mass. The homework for this week is a sheet to work out their weight on the moon and the various planets of the solar system. This site lists the proportional gravity of the different planets and calculates weight for them. You could also have your kid search out this information themselves if you feel they're up to it.
A number of kids left their sheet behind. We'll be open 4:00-8:00 Wednesday, 4:00-6:30 Thursday and 4:00-8:00 Friday if you want to drop by, otherwise they can pick it up when they come to class again next week.
We also discussed how if they were on the moon or one of the other planets their weight will be different because the gravity is different, which is based on the planet's mass. The homework for this week is a sheet to work out their weight on the moon and the various planets of the solar system. This site lists the proportional gravity of the different planets and calculates weight for them. You could also have your kid search out this information themselves if you feel they're up to it.
A number of kids left their sheet behind. We'll be open 4:00-8:00 Wednesday, 4:00-6:30 Thursday and 4:00-8:00 Friday if you want to drop by, otherwise they can pick it up when they come to class again next week.
Tuesday, December 3, 2013
This week at SET
Today, we finished up our discussion of orbits and Earth's tilt by discussing the impact of the moon on Earth's rotation and stability, and how the very creation of the moon involved an impact!
At the end of class, I also showed them some solar bodies to give them an idea of the scale involved when dealing with planetary bodies, because a lot of them were struggling with the size and weight of the moon, Earth and our sun. A quicker comparison of solar sizes can be seen here, with the advantage of keeping everything within the frame.
Despite the sun's immense size, from Earth it appears almost exactly the same size as the moon does, which is why Earth has the phenomenon of solar eclipses, something the other rocky planets around us do not. Mercury and Venus lack moons and Mars does not have a large enough one. You'd have to go all the way out to the gas giants to see eclipses on other planets, but if you did, they'd happen all the time. And although Pluto would seem a good bet for eclipses all the time due to its large, close moon and extreme distance from the sun, its odd orbit and rotation means it only happens every 120 years - but when it does, for several years Pluto experiences a eclipse about once a week.
In addition, a lot of the kids didn't know it's bad to stare directly at the sun. I explained that this permanently damages the eyes, but you may want to repeat that to them a few more times to make sure they remember.
For homework, look at the moon! The moon waxes (the lighted part grows bigger) until the side we see is all lit up, then wanes (the lighted part grows smaller) down to a new moon where it's entirely black. It isn't immediately apparent which direction the moon is going in, so look at it for a few nights in a row and see if it's getting bigger or smaller. If it's getting bigger, it's a waxing moon, and smaller is a waning moon.
(And our weather unit may have concluded, but there's always more interesting things to learn about! For example, there's a very hard to catch phenomenon of lightning bursts that go up from the clouds rather than down, producing a brief but beautiful effect known as sprites. For many years these were known only to a lucky few high-altitude pilots who glimpsed them and scientists weren't even sure they existed, but modern film has now managed to capture numerous sprites in increasing detail.)
Also, Christmas vacation is coming up. As you can see from the schedule we won't be meeting for the last two weeks of December, the 24th and 31st. That isn't the end of this session, however! Fall session for SET school continues meeting through January, with the spring session only beginning in February.
At the end of class, I also showed them some solar bodies to give them an idea of the scale involved when dealing with planetary bodies, because a lot of them were struggling with the size and weight of the moon, Earth and our sun. A quicker comparison of solar sizes can be seen here, with the advantage of keeping everything within the frame.
Despite the sun's immense size, from Earth it appears almost exactly the same size as the moon does, which is why Earth has the phenomenon of solar eclipses, something the other rocky planets around us do not. Mercury and Venus lack moons and Mars does not have a large enough one. You'd have to go all the way out to the gas giants to see eclipses on other planets, but if you did, they'd happen all the time. And although Pluto would seem a good bet for eclipses all the time due to its large, close moon and extreme distance from the sun, its odd orbit and rotation means it only happens every 120 years - but when it does, for several years Pluto experiences a eclipse about once a week.
In addition, a lot of the kids didn't know it's bad to stare directly at the sun. I explained that this permanently damages the eyes, but you may want to repeat that to them a few more times to make sure they remember.
For homework, look at the moon! The moon waxes (the lighted part grows bigger) until the side we see is all lit up, then wanes (the lighted part grows smaller) down to a new moon where it's entirely black. It isn't immediately apparent which direction the moon is going in, so look at it for a few nights in a row and see if it's getting bigger or smaller. If it's getting bigger, it's a waxing moon, and smaller is a waning moon.
(And our weather unit may have concluded, but there's always more interesting things to learn about! For example, there's a very hard to catch phenomenon of lightning bursts that go up from the clouds rather than down, producing a brief but beautiful effect known as sprites. For many years these were known only to a lucky few high-altitude pilots who glimpsed them and scientists weren't even sure they existed, but modern film has now managed to capture numerous sprites in increasing detail.)
Also, Christmas vacation is coming up. As you can see from the schedule we won't be meeting for the last two weeks of December, the 24th and 31st. That isn't the end of this session, however! Fall session for SET school continues meeting through January, with the spring session only beginning in February.
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