# Center of Mass Fork Experiment

Center of mass (COM) it’s easy balancing act or a trick to try at home! All you need is 2 forks, a quarter, a cup, and some patience.

Why does this look so weird? It all has to do with center of mass. COM is hard to define, but almost everyone has a great intuition for it! You find the COM of objects when you’re balancing things. Once an object is balanced, wherever you are holding up that object is where it’s COM is. You could probably guess where the center of mass is for a lot of symmetric objects. For example, a ruler’s COM is in the middle. But if you add some extra weight to the end, it’s COM will shift!

A fork is pretty asymmetic, and that shows in it’s COM.

If you try to balance 2 forks on your fingers, you probably won’t win. This is where things get weird– the center of mass does not necessarily need to be within the object! For 2 forks, it ends up being just right outside of it.

Which makes the “trick” work. If you stick something, like a quarter, between the 2, now the center of mass of this collection of objects is now on the quarter. You will intuitively find the exact place on the quarter where the center of mass lies, when you achieve balance on something like the edge of a cup (pro tip: the more rigid the edge of the glass is, the better. We used the bottom of the cup here because that was less rounded, and hence stuck better, than the top of the cup). There you have it! Rather than thinking of it as a trick, think of it as you showing a weird property of physics in a simple way!

# Can You Make Dry Ice Ice Cream!

You’ve probably heard of liquid nitrogen ice cream before. It’s made by mixing together ice cream ingredients with liquid nitrogen, which turns into a gas at -321º F. Learn more about that at https://www.thoughtco.com/cryogenics-definition-4142815. The intense coldness is what turns the ice cream ingredients from a liquid to a tasty solid.

So by this logic, you should be able to make ice cream by just adding something really cold to your ice cream ingredients. Solid carbon dioxide, AKA dry ice, is a good candidate to experiment with. To be a solid, carbon dioxide has to be at least -109º F! When you mix dry ice into ice cream ingredients, something interesting happens. It does cool it down, but you additionally get a lot of bubbles. As the carbon dioxide sublimates from solid to gas, little pockets of gas gets trapped underneath the ice cream, and they escape to the surface in little bubbles of CO2.

Why don’t these bubbles form with liquid nitrogen? Both dry ice and liquid nitrogen are turning into gases. But, it’s a lot easier for a solid to sink to the bottom of the ice cream mix than a liquid. When making liquid nitrogen ice cream, if you leave the nitrogen alone, you won’t see it sink down to the bottom of the ice cream. So when the liquid nitrogen evaporates, the gas simply rises from the top of the mixture into the room.

The little carbon dioxide bubbles that escape are the same as bubbles in a soda. That’s why it’s called carbonation! So in a way, you can create a sort of carbonated soft serve by mixing ice cream ingredients with dry ice– but be ready for it to be a bubbly mess.

Note: You should never ingest liquid nitrogen or dry ice. It will burn you and harm you. When people eat liquid nitrogen ice cream, they’re just eating the ice cream ingredients, with all the liquid nitrogen changing phase into a gas before consuming it. The liquid nitrogen merely acts as a mechanism to cool down the ingredients.

Written By: Amanda Williams

# Gravity Falling Experiment: Feather in a Vacuum!

Galileo once proposed that all objects under gravity, whether they’re really heavy or really light, will fall and accelerate downwards at the same rate. In a famous experiment, he supposedly dropped both from the Leaning Tower of Pisa and proved it.

Why is this true? For something with more mass, it does feel a stronger downward force from gravity.

BUT because of the mass, it’s harder for that thing to accelerate. (When you hear “accelerate,” think rate of falling).  So for something relatively heavy, the stronger pull of gravity and the toughness to accelerate it should perfectly balance each other out, causing things accelerate at the same rate. This fact is sometimes referred to as Newton’s 2nd Law.

The problem with this explanation is that it seems to defy what we see every day, right?

We dropped a penny and feather at the same time. You probably don’t need to do this experiment to guess what happens. The penny will hit the deck long before the feather.

It’s not that Galileo and Newton are wrong, it’s just that their model is simple; it doesn’t take the full picture into account. The secret here is that Newton’s 2nd Law only holds true if gravity is the ONLY force acting on the two objects. If objects fall through the air, then air resistance plays a part. And of course, some objects are more affected by air resistance, like feathers. To design a better experiment, we could try the same objects, but get rid of the air! We’ll use a vacuum chamber.

A vacuum chamber will suck out some air, creating less air resistance. The less air there is, the closer their rate of falling is!

If you had no air at all, if you could truly get gravity to be the sole factor, then you could call the object being in free-fall, and you would prove Newton’s 2nd law true. For this reason, the feather experiment was re-created on the Moon by astronaut David Scott using a feather and a hammer. It works because yes, our Moon has gravity (because it has mass) but it doesn’t really have air resistance, because there’s basically no atmosphere.

Written By: Amanda Williams

# Crush Your Cans With Science and Recycle!

September 27th is Crush A Can Day and it’s a day to serve as a reminder that we CAN recycle our aluminum CANS! We love recycling and we’ve got a hot way to do it, with the help of science.

This is an experiment we recommend doing at home! All you need is a can, water, something hot like a stove, and tongs to keep you safe. First, scoop a little water into the can. By heating up the can, water expands into steam. This steam starts taking up all the room in the can, pushing out air.

Seal the can with water. This causes two things:

1. The water cools down the steam, condensing it back into water.
2. Air can’t get back in the can.

If air can’t get back in the can, and the steam is now taking up a lot less room because it’s cooler and condensed, you’ve created a can with nothing much in it- a vacuum! Our atmosphere exerts pressure on us all day every day. Up in Idyllwild, around 5000 feet in elevation, our atmosphere pushes about 12 pounds on every square inch of us (AKA 12 PSI). We typically don’t notice this pressure because it’s everywhere and usually evened out. But, not the case with our vacuum-can! And so, the can gets crushed by the pressure of our atmosphere that’s always there.

We hope we’ve inspired you to recycle, and maybe experiment along the way!

Written By: Amanda Williams

# Can you change the color of oudin coil sparks?

An Oudin coil can take the energy out of your outlet and create sparks you can see! It’s sometimes called a mini tesla coil. The sparks on them usually look violet.

If you know the visible light spectrum, you might know that violet light is the most energetic color of light.

The oudin coil looks like it’s putting out a lot of energy, but there’s a different reason for the violet sparks. In fact, the color of the sparks don’t always have to be violet like most people see. To demonstrate, check out the oudin coil when it sparks in something else, like carbon dioxide. An easy way to get a bunch of carbon dioxide in one place is with its solid form — dry ice!

When surrounded by CO2, the sparks from this oudin coil are clearly a different color!

The reason for the color shift is because of what is surrounding the oudin coil. Our air is less than 1% carbon dioxide. When sparking in air, the coil surrounded mostly by different gases (mainly nitrogen and oxygen). The answer to why that makes a difference is the same answer as to why different gases glow different colors when you put a lot of energy into them.

If you split apart this light, with something like diffraction glasses, you’ll see each type of gas has a unique spectrum of light. The study and use of this phenomenon is called spectroscopy.

Spectroscopy is a way of identifying gases, and it’s how we know what far away things like stars are made out of! On a tiny molecular scale, CO2 and what makes up our air are fundamentally different, and will create differences we can see… if we are clever enough to notice. By playing with this oudin coil and looking at colors, we’re revealing secrets about a seemingly invisible world.

Written By: Amanda Williams

# Homopolar Motorcar

A homopolar motor is a device that relies on flowing electricity, magnetic fields, and the interaction between the two. It consists of a voltage source, neodymium magnets, and a conductor that allows electricity to flow. And it’s super easy to make yourself!

What you’ll need:

• 1 AA battery
• 2 neodymium magnets
• Thick copper wire

————

Step 1

Place one of your magnets onto the positive terminal of the battery.

Step 2

Use the already attached magnet to test the poles of the second magnet. Figure out which sides are repelling each other, and place the second magnet so that the repelling side faces away from the battery. This way, either both South poles or both North poles are facing outwards! (Note: it doesn’t matter which, as long as they’re consistent with each other!)

Step 3

Shape your copper wire so that it can hook easily on the inside of the magnets. Try to maximize the amount of contact it has with the magnets on BOTH sides, so as much electricity as possible can flow. When it’s been properly shaped, hook the wire onto the motor!

Instead of using a wire, you could use a sheet of aluminum foil! Lay it as flat as you can on a level surface, away from any metals that might attract your magnets. Make sure there are no tears or holes in the aluminum. Then place your battery-magnet motor on top! The aluminum will allow electricity to flow!

————

When a magnetic field is applied to an object carrying electricity, it applies a force to that object. This is called the Lorentz Force. Due to the electricity flowing through the magnets, this force becomes a torque, causing the motor to rotate and drive forward!

Written By: Scott Yarbrough

Artist: http://www.twinmusicom.org/

If you’ve taken our Electricity and Magnetism class, you’ve seen this device before! You press a button and an electric arc rises to the top of two tall wires. This is the Jacob’s Ladder! But what’s happening here?

The base of the Ladder is a transformer — a device that changes an incoming voltage. In the Ladder’s case, it increases it by a huge amount. That voltage is put into one of the vertical wires, increasing its electric potential. The electricity needs to flow somewhere, so it ionizes the air to jump to the other vertical wire. As the electricity arcs, it heats up the ionized air, which causes it to rise. As the wire get further apart, it becomes more and more difficult for the electricity to reach, and the arc eventually stops. Then the transformer builds up the electric potential again, repeating the process all over again. Though as electricity flows through the wires, they heat up. The hotter they are, the slower the electricity flows. Eventually, you’ll notice the arc having trouble getting to the top as it travels slower and slower.

This is just one of the many cool electricity demos we have at AstroCamp! Be sure to check out this and all the others on your trip.

Written By: Scott Yarbrough

# What is Ferrofluid?

Back in the early 1960s, a fledgling NASA was presented with lots of new problems. Going to space was unlike anything humans had ever done, and engineers and scientists were constantly searching for answers to issues they had never even considered before.

One of these problems was dealing with the properties of a liquid in low-gravity environments. On Earth, a liquid will stay at the bottom of its containers as gravity pulls it down. But without gravity, the liquid will float all around its container, forming spheres of liquid.

Since the rockets used by NASA relied on liquid fuel, there was a problem getting the fuel pumped to the engines once the spacecraft was in orbit. Several ideas were tried, and though NASA eventually settled on small solid rockets to settle the liquid fuel near the intake, one of the ideas proposed by a scientist named Steve Papell was a ferrofluid fuel.

A ferrofluid is any liquid with metallic metal suspended in it. The metal has a special material coating to prevent the small pieces from attracting or repelling each other, but when the solution is exposed to an exterior magnetic field, the ferrofluid is attracted to the magnet. It also increases in density and becomes somewhat rigid.

When Steve Papell suggested using a magnetic fuel, his idea would be to control the flow of the fuel by using magnets. Instead of letting the

liquid blob in the center of the tank, it could now be held towards the fuel intake and make the system more efficient. Though it was a good idea, NASA found other, better solutions for the rocket issue.

That didn’t mean the end of ferrofluids, however. Another scientist named R.E.Rosensweig improved upon the design and developed a new branch of fluid dynamics known as ferrohydrodynamics.

Since then, ferrofluids have been used in many devices — the most common of which is in electronic devices such as hard disks, using it to form liquid seal that will be held in place by magnets. This seal prevents dust and other materials from entering the hard drive.

Despite its practical uses, ferrofluid is just cool to look at. If you ever have the chance, grab a magnet and play around with it!

Written By: Scott Yarbrough

# Pendulums and Gravity

In the video above, I talk about how pendulums actually work. If you haven’t watched it, the principle is simple: an object is suspended from a fixed point and allowed to swing back and forth – the mass of the object and the time it takes to swing back and forth are independent of each other, relying only on the length of the string and the strength of gravity.

Normally, you’d think of gravity on Earth’s surface as being constant, but the Earth isn’t a perfect sphere, meaning that the force of gravity near the equator is slightly weaker than at higher or lower latitudes. And how did we discover this fact? Pendulums!

In the year 1671, a French scientist named Jean Richer travelled to French Guiana. Among several experiments and astronomical observations during his two-year trip was to take measurements with a clock pendulum.

He set up the pendulum in the same way I did in my video, but he adjusted the length of the pendulum so that one half-swing took exactly one second, a common technique at the time. What he found was that the pendulum length needed to be slightly shorter than it did back in Paris, by about 3 millimeters. Though a small difference, it was significant enough to begin a discussion about the varying gravitational field of Earth.

This was later proved by Isaac Newton by determining that due to the Earth’s rotation, it was thicker at the equator, meaning the surface was further away from Earth’s center of mass. This was further supported by Newton’s idea that gravitational force decreases as the distance between two objects increases.

Scientists started to use pendulums to take measurements of the gravitational field in other locations and began to create a model of the Earth’s true oblong shape. Since then, we’ve developed more accurate methods to measure the same thing, but they were pioneered by those first efforts.

Written By: Scott Yarbrough

Video Music: Funky Chunk Kevin MacLeod (incompetech.com)

# Bubble Hurricanes

CAUTION: This experiment uses a hot plate. Please use adult supervision if attempting to recreate.

Bubbles are a great resource for fun and physics. They provide interesting insight for optimization and can even be used as models for atmospheres. Scientists are able to use bubbles as models for the atmosphere because they are very thin compared to the sphere they enclose, just like Earth and it’s atmosphere!

To show this, you can do a very simple experiment, but be sure to have supervision since there is a risk of burn. All you’ll need is a stove top, a metal dish, soap, and a straw. Heat up the metal dish, pour a soap solution on top and blow a bubble into it, using the straw so as to not burn yourself.

You will be able to see vortices form in the film of the bubble. These vortices mimic those of how hurricanes and cyclones form. As the soap film is heated up from the bottom the vortices are formed. The strength of the vortices intensify then die in a uniform way. This is due to convection currents.

Convection currents are the transfer of heat by the mass movement of heated particles into an area of cooler ones. Convection currents on Earth is what causes things like weather and storm patterns. The hotter the planet gets, from geothermal heating and climate change, the more intense weather we will experience.

The same phenomenon can be clearly seen in our bubble hurricanes. The hotter the soap solution becomes, the more intense the vortices will be, but they also die out much more rapidly.

Credit: University of Bordeaux in France

Written By: Mimi Garai

### 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!