# Leiden-frost Nipping at Your Toes

Have you ever played air hockey? There is something strangely satisfying about how the puck slides effortlessly across the table, before finally coming to rest. This same thing happens naturally as well, and it’s actually some pretty cool science. Lets check out how it works!

When things of different temperatures interact, the warmer object loses its heat to the cooler object. This simultaneously warms up the colder thing, and cools down the warmer thing. This shouldn’t be surprising. It’s the reason that snow melts in your hands and make your hands feel cold. However, when things are of vastly different temperatures, it can get a little strange.

In the video, we are dripping water onto a stovetop that is around 500℉. The water is only about 50℉, but the important part is that the boiling point of water is around 200℉ (technically 212℉ but AstroCamp is at an elevation of about 5600’, which actually lowers the boiling point to about 202℉) which is much lower than the temperature of the stove.

When the drops of water hit the stove, the part that hits first is immediately vaporized because of the difference in temperature. This means that the little droplet of water now has a little barrier of water vapor between itself and the stovetop, which it can float around on. The water droplets seem to bounce and skitter around without boiling away. This is what we call the Leidenfrost Effect. For water, this seems to occur at temperatures of at least 400℉.

It is the same thing that allows a person to pour liquid nitrogen over their hand unharmed (Don’t try this at home, but you can see it below), or dip their hand in water and then dip it in boiling hot lead (DEFINITELY don’t try this at home)!

Heat rises, boats float, clouds hang listlessly in the sky, and icebergs aimlessly bob around the ocean. All of these things happen because of the same scientific property: density!

Density is a rather simple property. It depends on two things, mass and volume. Mass is basically how much something weighs, but something still has the same amount of mass weather it is on Earth, Jupiter, or out in space where its weight would change dramatically. Volume doesn’t have anything to do with how loud something is, but rather with how much space it takes up. Mathematically, an object’s density is equal to its mass divided by its volume.

The demonstration here using the pipette in a bottle of water is a great way to buoy your own understanding of density. The pipette is carefully balanced to barely float in the water. However, by squeezing the bottle, water is forced up into the pipette. This makes the pipette heavier, which raises its density. Releasing the bottle down the opposite. For another cool example of density, click here!

By simple comparing the density of different things, we can tell if they would float or sink in water or air or anything else that has a known density. This is incredibly useful and can lead to some fun facts. For example, Saturn is less dense than water. That is to say it would float in a bathtub, but it might leave some rings! Red giant stars, like the famous Betelgeuse, are actually less dense than air! They are incredibly heavy–Betelgeuse weighs in at about 18 suns worth of mass–but they take up so much space that they are essentially GIANT balloons!

The sun would not float like a balloon now, in fact it is currently much more dense than water. However, given 5 billion years it will enter the red giant phase of its own life and grow in volume by about 800 million times! This will decrease its density so much that it goes from 40% higher than water to lower than air! As you can clearly see, density is not necessarily a constant property of something, it is actually something that can change.

One of the most commonly accepted consequences of density is that heat rises, but that isn’t technically true. It would be more correct to say that heat rises on Earth. This is because as things warm up, their volume increases which lowers their density. However, if we leave the friendly confines of Earth, this is no longer true! In the microgravity environment aboard the International Space Station, there isn’t really an “up” or “down”, gravitationally speaking. That makes it hard to decide what “heat rises” even means! Fire gets equally confused. Check out this comparison between fire on Earth and aboard the ISS from NASA.

# DIY: Fascinating Properties of Dihydrogen Monoxide

Humans are approximately 60% dihydrogen monoxide. If this is alarming, it might be helpful to know that this is just waterWhile water is certainly something quite familiar, it has a lot of properties that are very important and they all come from its famous chemical formula, H2O. Let’s take a look and try to understand a few.

Water molecules−which you can see an illustration of on the right−are made up of one Oxygen atom and two Hydrogen atoms. When atoms are bonded together, they do so because of electric charges. In this case, each hydrogen atom has one electron that it shares with the oxygen atom. Electrons carry a negative charge, and are held closer to the oxygen atom. This gives the oxygen atom a negative charge while leaving the hydrogen atom slightly positive. As you have almost certainly hear, opposites attract. These opposite charges pull on one another which keeps the water molecule together amidst a microscopic sea of atoms.

Due to this and the shape of the water molecule, each has a negative part where the oxygen is and a positive part where the hydrogen is. Scientists call molecules like this polar, and it is this polarity that gives rise to many of water’s unique and important properties!

The polar water molecules orient to one another and are held together by the electric attraction of opposite charges, which you can see in the illustration above.. This is important for us: If this were not the case, water would not be a liquid at room temperature at all! The relatively light water molecules would fly off as a gas because the molecules would have no attraction between them. Without this very important property, there would be no life as we know it. This attraction of water molecules to one another is called cohesion. They can also stick to many other objects by the same process, a property known as adhesion.

These two properties come together in the video above. The water molecules stick to the string, but also to one another. This allows the water to be poured at strange angles, and none of it would happen if it wasn’t for that fascinating little molecule, dihydrogen monoxide.

# What’s the Matter: Is Fire a Plasma?

Is fire a plasma? Turns out it’s not a trivial question! The answer depends on how you define the parameters of the fourth state of matter. Descriptions of plasma commonly include the following points: plasma is what happens when a gas is subjected to lots of ionizing energy. Although thoroughly ionized, it is quasi-neutral. Its molecules display collective dynamics and respond as a group to electromagnetic influence.

The sun as seen by NASA’s IRIS orbiter. Ultraviolet image translated into false color for human consumption. Stars, including our sun, are made of plasma.

Most of the observable universe is made up of plasma! Astrophysical plasmas are mind-blowingly hot. On Earth, too, plasma is created by copiously applying heat or otherwise energizing a gas, although plasmas can also be created in laboratory scenarios that are cold by human standards.

So, which state of matter does fire belong to? Depending on who you ask, a flame is either a low-level plasma or a lightly ionized gas. A flame is a heated volume of air in which some electrons have broken free from their nuclei, but it’s not hot enough (or ionized completely enough) to enable cohesive electrodynamic behavior on the level of, say, an arc welder.

Plasma or not, the gas within a flame contains enough ions to make it a decent electrical conductor! Here, electricity arcs from a generator to a candle flame.

# Collisions!

Newton said that for every action there is an equal and opposite reaction.  Collisions are the thing that happens when two objects slam into each other!  But what does that mean for science?  Well, depending on the object’s material(such as using silly putty vs using marbles, skee balls, or shots), mass, and vector (magnitude and direction) it can mean a few things.  There are two different types of collisions that we can witness on a daily basis.  Inelastic and elastic collisions.  An inelastic collision is a collision that has a conservation of momentum, but not kinetic energy.  Whereas an elastic collision conserves both kinetic energy and momentum.  There are different types of energies.  Kinetic energy can be thought of as “moving” energy.  There is also potential energy, rotational, thermal, gravitational, chemical…the list goes on.

Momentum is defined as the strength or force that something has when it is moving. Most ordinary collisions that you witness are considered inelastic because of the sounds you hear (sound=type of energy -> total kinetic energy – sound =loss of kinetic energy), or the heat released (same as above)..  The most elastic-like collision is when two billiard balls collide (or like in our experiment)  they are technically inelastic collisions because the loss of energy in the sound, but that energy is negligible (meaning that it doesn’t matter a whole lot).

To play around with different outcomes of mostly elastic collisions you can change a few variables such as mass, density, and velocity (speed and direction).  We used some similar sized objects, and then some extremely different sized objects to test this out.  We also changed the angle of impact to see where the different objects would end up after impact.  It turns out that a slight angle change makes a big difference due to the curvature of the balls.  This is something that professional billiards players have to take into account at every shot.  The speed of the objects just before impact makes a huge difference also. If you try to collide the two objects with a slow enough velocity then the objects may just travel together.  On the other hand if you slam them into each other you might see that there is a nearly complete transfer of the kinetic energy from the first object to the second.

### WELCOME TO OUR ASTROCAMP BLOG

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!