The simplest invisible inks consist of organic compounds like lemon juice, vinegar, diluted honey, and even white wine– all substances that subtly weaken paper fiber. Once the liquid dries, it’s undetectable under normal circumstances. Apply heat, however, and the hidden message seems to appear out of nowhere.
Organic ink makes the painted area more susceptible to oxidation. When it’s heated, it browns before the rest of the page. If you try this at home, keep a close eye on the developing ink, and be careful not to actually set the paper on fire!
For an even more dramatic hidden ink DIY, paint your message in laundry detergent (dilute if necessary to make the ink invisible), then expose it to a blacklight. Your missive will glow!
Modern invisible inks take advantage of chemical reactions to hide, then reveal, secret communication. Phenolphthalein, for instance, is perfectly clear except in a slightly basic environment. Between pH 8 and 10, it turns pink! A dilute solution of this chemical makes a great hidden message medium– just spray it with watered-down ammonia to see the concealed writing take shape.
Note: phenolphthalein is toxic and should only be handled with proper safety gear and training. As always, ask for adult permission and have a fire extinguisher on hand when experimenting with heat & flames. Last but not least, have fun! Happy April Fools Day from Astrocamp!
Did you know that astronauts on the International Space Station (ISS) experience about 90% of the gravitational acceleration that we feel on Earth’s surface? That might seem strange, especially since when we look at them, they are always floating around. While this makes it tempting to say that there is no gravity in space, that is quite clearly very far from the truth, so why do they float1?
On Earth, we are pulled down towards the Earth at 9.81 meters per second squared, meaning that if we weren’t pressed up against the ground, our speed would increase by 9.81 meters per second every second! This is known as free fall. This is something that can be experienced during the initial phase of a skydive, during turbulence in an airplane, or while going down a steep part on a roller coaster. It is often accompanied by a weird queasy feeling in the stomach.
By taking a water bottle and drilling some holes in it, we can see why the astronauts are weightless. Both the bottle and the water are being subjected to Earth’s gravity. When the bottle is held still, the water falls out through the holes because gravity is pulling it down. Then, when the bottle is released, they are both pulled down at the same rate. With no difference in acceleration between them, the water floats happily inside the bottle and doesn’t go out the holes at all.
This is actually what is happening to those astronauts. When something is in orbit around the Earth, it is being pulled down by the force of gravity. For the ISS, this is about 9 meters per second squared! If the ISS wasn’t moving above the Earth, it would fall to the surface in less than an hour. However, Astronaut Scott Kelly was just on board for a year and didn’t plummet to his fiery doom. This is because the ISS is not staying still. Not even a little bit.
The ISS goes at about 17,000mph, which is over 10 times the velocity of a speeding bullet. This is entirely necessary, because as gravity yanks the ISS down towards the surface, the space station has moved far enough to miss the surface. This balance is very precarious. If the ISS were going faster, it would instead get farther away from the Earth each time and escape into space. If it were going slower, it would constantly get closer to the Earth, which is not what we want2.
How do astronauts train to get used to this? Let’s go back to the water bottle demonstration again. Take a second to think: What would happen if instead of just dropping the water bottle, we threw it up in the air? Let’s take a look!
While you might think that the water will come out on the way up and stay in on the way down, it instead turns out that the water stays inside the bottle from the moment it is free of the hand. This means it is also in freefall while it is going up, which seems strange, but both the water and the bottle are subjected to the same gravity with no other outside forces for the same time. To train the astronauts, they do the same thing, but with an airplane. This plane, cleverly and unpleasantly known as the Vomit Comet, flies up and then coasts through the air, allowing it to continue up in a similar trajectory to the bottle. Then, before it hits the ground, the pilots pull up and go skyward for a bit before repeating the process again. As you can imagine, it’s enough to make anyone a little queasy3.
1Image: Satoshi Furukawa floats aboard the ISS. Photo credit: NASA 2This is a real issue. The ISS slows down slightly due to the outer reaches of the Earth’s atmosphere. As a result, they use thrusters to get back up to speed about once a month! 3Image: Trajectory for the Vomit Comet. Courtesy of NASA
Electric generators change mechanical energy into electrical energy. An electric motor does the opposite: it changes electrical energy into physical motion. This conversion is possible because of the Lorentz force.
Electricity is just the movement of electrons through a loop, called a circuit. Ever notice how magnets can repel or attract objects without touching them? When a circuit carries electrons near a magnet, the magnetic field pushes those electrons sideways.
The Lorentz force is strongest when the magnetic field and current-carrying wire are perpendicular to each other. Electric motors use this arrangement to turn electrical energy into mechanical motion efficiently. It’s easy to see for yourself, too! All you need is a magnetic field and a circuit that’s free to move. In today’s experiment, we’ll show the Lorentz force in action with a magnet, a battery, and a length of wire.
Start by setting the negative end of an AA battery on a strong magnet. Magnetic field, check; power source, check. Mold a length of wire into any shape that can balance on the positive end of the battery while also touching the magnet, completing a loop of conducting materials. Given a circuit to flow through, electrons begin to move, and voila! You’ve got a current flowing through a magnetic field. The current and the field are nearly perpendicular to each other where they intersect. The Lorentz force pushes the electrons, and the conductor they flow through, off to the side.
Shape the wire so that it can balance and spin on the positive terminal, and the electromagnetic push induces rotation for as long as the battery’s charge lasts. Electrical energy becomes physical motion. Congratulations– you’ve just created a motor!
As far as we can tell, the ocean has been slightly basic for hundreds of millions of years. However, that seems to be changing, and the culprit may surprise you. Everyone has heard of carbon dioxide. It’s the thing we breathe out, what plants crave, and there’s this thing called the greenhouse effect which you’ve probably heard of by now.
CO2 concentrations have certainly changed in the past based on our examinations of ice core samples. However, they are certainly on the rise now. Credit: NASA, UCR, RUSD
What we do know for sure, is that carbon dioxide is on the rise. While the most often talked about consequence of this is a trend of increasing global temperature, there is another important concern, and it has to do with our water. There are many ways that we can measure water including temperature, pollutant content, clarity, and salinity, but this particular issue focuses on acidity.
Water is made up of two parts hydrogen and one part oxygen, leading the the chemical formula H2O. In pure water, these molecules occasionally break apart due to the following reaction:
On the left side, we’ve got our old pal water. In the middle, the double sided arrow means that this reaction can go both ways, depending on the ratio of water to its parts. Pure water is neutral, meaning that this reaction is the only source of H+ and OH– ions1 in the water. If anything throws this balance out of whack, the water will become basic if more OH– ions are added, or acidic if more H+ ions2 are added.
So what does all of this have to do with carbon dioxide (CO2)? When the CO2 gets in contact with water–which covers most of the Earth–it combines with the H2O by the following reaction.
This forms Carbonic acid, which then donates its extra hydrogen to the water like this:
In the previous paragraph, we talked about how anything that can add H+ to the water will cause it to become acidic. The resulting molecule above is known as carbonic acid because it has these extra hydrogen ions to donate.
While this all seems pretty abstract, you can watch it happed below. This water is poured over dry ice or solid carbon dioxide. Solid carbon dioxide turns directly into a gas at room temperature. The water also has an indicator solution that will cause it to turn from neutral green to red if it is acidic, and blue to deep purple if it is basic.
We measure this using the PH scale, which runs from zero to 14 with low numbers indicating higher acidity. It is also a logarithmic scale, which means that changing from a seven to a six on the scale corresponds to an increase of ten times to the acidity! For the past 300 million years, the ocean has been at a steady–and slightly basic–PH of 8.2. Over the past 200 years, it has dropped to about 8.1, which doesn’t seem like much on this scale, but corresponds to an increase of about 30% to the number of acidic ions in water. Even without further increase to atmospheric CO2, this trend should accelerate to a PH of 7.8 by the year 2100, an increase in acidic ions of 126%!
What does all of this mean for us living on Earth? No one is quite sure. Most organisms can only tolerate a narrow range of acidity, and there are many species that live in the ocean. Simulating these conditions in a lab is pretty easy, so we can identify some at risk species right away. Coral reefs, in particular, are known to be very sensitive to acidification.
Dissolved carbon dioxide can interfere with the calcification process that allows shells and exoskeletons to grow. Over the course of 45 days, this sea butterfly slowly dissolves in a lab simulation of acidic ocean water. Courtesy of David Littschwager/National Geographic Society. Similar research continues today.
Ions are just atoms or groups of atoms with a net charge, meaning they have an extra electron if negative, or lack an electron if positive. Ions are much easier to dissolve in water than neutral molecules.
Note: The freed hydrogen ions will actually combine with surrounding water molecules, forming Hydronium (H3OH+) which is usually denoted H+.
Why is it so hard to pick the perfect bracket? Let’s take a look at the mathematics of March Madness!! This year’s complete printable March Madness bracket by ESPN.
It all comes down to probability. Let’s start by making things simple before we truly delve into the madness. Imagine two perfectly even teams are about to play a single basketball game. Each team is equally likely to win. Who is going to win? Quite clearly in this scenario, anyone would have a one in two shot to get the winner right. In this simple one game bracket, you would have a 50% chance of having a perfect bracket!
In the NCAA tournament, there is a field of 68 teams. Only one team can win, and one team is eliminated in each game, meaning there 67 games must be played. If each team were evenly matched (we’ll deal with the alternative in a moment), then the odds to pick the winner of every game correctly is a paltry one in 267, or one in 147,573,952,589,676,412,928. That’s over 147 quintillion! Not coincidentally, these are the same odds as picking heads or tails on a flipped coin 67 times in a row1.
Fortunately, most brackets don’t deal with the play in games, meaning they consider the field to be 64 teams, requiring 63 correct picks for the elusive perfect bracket. In addition, the top team in each region has never lost to the bottom team, giving four more games that stand as pillars of stability amongst the madness of March. Assuming this holds true, our odds have just improved tremendously to one in 259 or one in 576,460,752,303,423,488! This number also looks humongous, but the odds of a perfect bracket have improved by a factor of 256 (or 28)!
Probability has not been kind to President Barack Obama in his quest for the perfect bracket either. Photo credit ESPN
Of course, not all of the teams in March Madness are the same. Each one has its own players, strategies, strengths, and weaknesses. If someone really followed basketball, they might be able to use these to their advantage. Actually, that’s kind of the point! After all, knowledge is power, so let’s see how that knowledge holds up against the mighty bracket! If in each matchup, one team held an edge raising its win probability to 60% and someone knew enough to identify every one of these teams, the odds of each favored team winning is as follows:
That’s still only one in 12 trillion–about 100 times worse than your odds of winning the Mega Millions jackpot! Here is where some of the struggle of the perfect bracket comes from. Even if each game has a favorite, the odds of the favorite always winning are not favored. The far more likely scenario is that some teams slip…but how can you tell which ones? So far, the answer has been resounding:
𝜫 is the ratio between the diameter and the circumference of a circle. Any circle. It doesn’t matter how big or small a circle is, this ratio is always the same. This may not seem incredibly important, but many things are circular or spherical. This results in 𝝅 showing up in all kinds of equations in science and math.
One especially weird thing about this number is that it is irrational. Most numbers can be written as a fraction, like ⅗ or ⅔, but irrational numbers just don’t fit not matter how big the top and bottom numbers become. Computers have calculated 𝝅 to billions of digits, and even in that expanse of numbers, no pattern seems to emerge.
𝜫 isn’t the only irrational number. Another famous one is e which is approximately 2.71828 but similarly continues on forever with no pattern in its decimal places. Unfortunately, “e day” is a much less celebrated hlid, probably because it doesn’t share its phonetic name with a delicious dessert. It also doesn’t have such a nice definition as 𝝅’s simple ratio. Instead, e is the result of the the following series:
Where things get especially weird is when this numbers are put together with another famous number, i. As you may recall, i is an imaginary number, which has a value of sqrt(-1). In school, many students ask how this number can possibly be important if it is imaginary. Well, look at this:
Woah! This happens because both e and 𝝅 are important for the mathematics of waves. To learn more, check out Euler’s formula, preferably over some pie!
As noted previously, 𝜫 is important because of its relationship with circles. It seems appropriate that we consume some pleasantly round delicious phonetic namesake to celebrate!
Why does water form lakes and oceans underneath a vast expanse of airy sky? The answer to that, and many more questions, is density! Density is most easily described mathematically by the following equation: This means that density depends on only these two quantities: Mass, or the amount of matter that something is made up of, and volume, a measure of how much space it takes up.
Most of us have heard of density in relation to things floating in water, but it also works for air. Seeing whether or not something floats in another thing is a great way to compare the density of two substances. Here, we can see that a balloon filled with nitrogen is more dense than air. Air is mostly made up of nitrogen, so it is mostly the additional weight of the balloon itself that causes it to fall to the ground. Alternatively, the helium balloon floats upwards as it is so much less dense than the surrounding air that the comparatively heavy rubber balloon is dragged up along with it. These two objects have the same volume, but their densities differ because of their mass.
The other quantity that we can look at is volume. If the volume becomes smaller, but contains the same mass, the density will increase. Alternatively, increasing the volume will decrease the density. In this demonstration, we take advantage of a property of gases described by Charles’s Law, which states that if we change the temperature of a gas, its volume will change proportionally. By lowering the temperature of the helium balloon with liquid nitrogen, we decrease its volume. This raises its density to be above that of air…until it warms up and expands back to a low enough density to again take flight!
This concept can help to explain many things, even if they seem odd at first. Clouds are made of water, but hang in the sky! It might seem like this is just because clouds are light, but the average cumulus cloud weighs over 1 million pounds! That is definitely not light, but they are light for how big they are, and they are big. Clouds are made up of water, but this water is very spread out. The volume is so big that this 1 million pounds of cloud actually weighs less than an equal amount of air would, even though we always think of air as being pretty light!
However, as this air rises it cools and gets closer together just like the balloon dunked in liquid nitrogen. Eventually, these water molecules band together as they get cold. When enough of the molecules stick together, they get to be more dense than the cloud around it, and plummet back to earth as precipitation.
By the way, the average person is a little less than a thousand times more dense than air. This means if you were 10 times taller, wider, and thicker but not any heavier, you would float like a balloon! Please don’t try this at home.
What sorcery is this!? Science it turns out! This is a great example of Bernoulli’s Principle! In short, this states that moving air has a lower pressure. Imagine trying to dig a hole in a pool of water: as soon as some of the water gets moved out of the way, the surrounding water rushes in to take its place. Air does the same thing!
The cup and straw demonstration shows this nicely, and it’s also a great experiment to try at home! By taking each apparatus and blowing into it, we can see there is a pretty huge difference.
The cup without any holes in the sides actually holds onto the balloon, which is weird, but makes sense. Inside the cup, air is moving quickly. This causes a lower pressure inside the cup than outside, and air that tries to fill up the space suctions the balloon in place. Alternatively, the cup with holes in the sides allows the surrounding air to help out. Very similar to the Bernoulli Bag, nearby air joins in creating a larger column of air that can lift, and even suspend, the balloon.
We know this looks like a trick, because it’s hard to tell from watching that he is exhaling vigorously in both cases. If you don’t believe us, definitely try it yourself!
Blowing air through a straw makes a small amount of air move pretty fast. A leaf blower makes a lot of air go really fast! When we add the beach ball, this air rushes around it at high speeds, making a low pressure. Surrounding air is then drawn in from all sides, which holds the ball in place.
While it might look like this is just well balanced on a spout of air, this idea falls flat when the angle of the leaf blower is changed. In moving to this orientation, the science stays the same–rushing air still causes the surrounding molecules to rush in and offer support on all sides–despite it looking like magic to the untrained eye!
The universe is full of action at a distance.Planets and stars tug on each other via the gravitational force. Magnets attract or repel based on their polar orientation. An object’s area of influence is called its field. Gravity, electricity, and magnetism are some of the most common field interactions.
The plasma ball’s central electrode transmits an electromagnetic field that extends far beyond its glass shell. Need proof? Try holding a fluorescent light tube nearby. The field generates electricity by setting electrons in motion, lighting the bulb!
Inside the globe is a miniature atmosphere of noble gases. These are less dense than air and ionize at relatively low voltages. At the core of this noble cloud, a high-frequency oscillating current creates a large buildup of negative charge. Like charges repel each other, so the buildup discharges outward in lightning-like plasma filaments.
Plasma is the most abundant state of matter in the cosmos. Solids, liquids, and gases are more familiar on Earth, but in the big picture, plasma is everywhere! It’s what stars are made of, and stars comprise most of the known mass in the universe. So, what is this stuff?
Adding energy to a solid weakens the attachments between its molecules, so it melts into a liquid. Add even more energy, and the molecules detach completely– that’s a gas. Plasma is what happens when a gas becomes so highly energized that electrons actually separate from their respective atoms, creating an electromagnetic fluid.
Bring gravity and rotational dynamics into the mix, and some crazy field patterns emerge. The NASA image at right shows the sun’s magnetic field lines. This behavior is the source of stellar weather like sunspots and solar flares, which have measurable effects on GPS and other systems. Large coronal mass ejection events can even blow out power grid transformers on Earth! Aerospace engineers, pilots, and electrical companies get forecasts from the NOAA Space Weather Prediction Center just like most of us check the weather at home.
We would like to thank you for visiting our blog. AstroCamp is a hands-on physical science program with an emphasis on astronomy and space exploration. Our classes and activities are designed to inspire students toward future success in their academic and personal pursuits. This blog is intended to provide you with up-to-date news and information about our camp programs, as well as current science and astronomical happenings. This blog has been created by our staff who have at least a Bachelors Degree in Physics or Astronomy, however it is not uncommon for them to have a Masters Degree or PhD. We encourage you to also follow us on Facebook, Instagram, Google+, Twitter, and Vine to see even more of our interesting science, space and astronomy information. Feel free to leave comments, questions, or share our blog with others. Please visit www.astrocampschool.org for additional information. Happy Reading!