Warning: Don’t do this at home!
When a scientist decides to play an April Fools prank on someone, it gets pretty serious. We pull out all the stops. One experiment that is guaranteed to both terrify and delight is the classic alcohol money burn.
The experiment is pretty simple. Mix some rubbing alcohol and water until your solution is about 50% alcohol. Take a bill (we would recommend a small one in case something goes bad) and dip it into the alcohol. Get any excess liquid off of the bill so that it isn’t dripping, Light it on fire!
The amazing thing about this experiment is that the money doesn’t actually burn. The fire goes out after a few seconds and the bill is unharmed. April Fools! But why? The secret lies in the water. The water mixed in with the alcohol is what is absorbing the heat of the fire, not the money. If the bill was soaked in pure alcohol it would be roasted in seconds. But water has a really good specific heat, meaning it takes a lot of energy to heat it up. The alcohol doesn’t burn hot enough to overcome this specific heat, and as a result the money stays safe.
The balloon in the video isn’t anything special. It’s a completely normal balloon filled with completely normal water. However, water is quite extraordinary!
We describe matter by listing its different properties. Some of these properties include how dense something is, its flexibility, its ability to conduct electricity, and even its color! Another less commonly known (but just as important!) property is called “specific heat”. This property is one of the things that makes water really interesting!
Specific heat indicates how difficult it is to heat up or cool down an object. For example, if you were to put two pots on a stove and fill one with air (by leaving it empty) and fill one with water, the air one would heat up much quicker even though the stove is adding the same amount of energy to each one! The water doesn’t heat up nearly as much while being given the same energy, meaning it has a very high specific heat.
This is exactly what happens in the video. The match is hot enough to melt the rubber and form a hole, causing the balloon to pop immediately! It actually pops before the fire even reaches the surface.
With the water balloon through, the entire balloon can be engulfed in flame, and nothing happens! This is because the water absorbs the energy from the hot flame, but doesn’t heat up very much. The rubber never heats up enough to melt.
Specific heat works the other way too. Water also takes a long time to cool off. In this way, the specific heat of water actually shapes the climate on a global scale. Take a look at the image below. The snow cycles are much more visible in the Northern hemisphere because they only have to go over land. Ground has a lower specific heat than water, so during the winter it cools down more easily, allowing the cold to pass further south forming ice over most of the Northern continents. In the Southern Hemisphere, the water is much more difficult to cool down, and the icy chill barely even reaches the land!
“A Breathing Earth” by John Nelson, using images from NASA’s cloud free satellite imagery of Earth.
Using a hair dryer to levitate a ping pong ball is a classic do it at home science experiment. It utilizes two basic principles to keep the ball hovering in the air. The first principle is the transfer of momentum from the moving air particles to the ping pong balls. Basically, the moving air hits the ball and exerts a force upwards on the ball. This is fairly intuitive straightforward. Bernouli’s Principle is the law responsible for keeping the ball contained in the airstream and it is much more complex and interesting.
Bernouli’s principle states that the faster a fluid or a gas move around an object, the less pressure they exert on it. What this means for the ping pong ball is that as the air moves around it, there is less pressure pushing on it from the sides. However, if the ball tries to leave the airstream (because of the collisions from the moving air or due to gravity) it will encounter some stationary air that exerts a higher pressure back on the ping pong ball. Essentially the ball is encountering a wall of static air that bounces the ball back into the airstream. Now because the wall is made of air it doesn’t take too much force to break the barrier, but as long as you keep the hair dryer fairly steady you should be able to keep the ping pong ball levitating for a while. Sadly there were no hair dryers back in Bernouli’s day, but we’d like to think he would have fun with this experiment if he did. Enjoy!
CDs are dying. It’s an unfortunate but inescapable fact as the world transitions to digital downloading. But while the end may be in site for CDs and DVDs, it hasn’t come yet. Before that day actually comes, perhaps we should take a quick look at this awesome technology and how it works.
A CD’s base a a polycabonate plastic material that is transparent. It provides the structure and protection for the layers above it. Above the polycabonate is a thin layer of aluminum reflective coating followed by another thin layer of crylic and then the label. The most important part of a CD is that the polycabonate sheet is imprinted with a series of miniscule bumps. The details of the bumps is a code that is what stores the data on the disc. The bumps move outward from the center of the CD in a spiral pattern all the way to the edge. The CD reader move along this track using a precise laser to detect the changes in the bumps and decode the data stored on the CD.
As CDs become less and less useful, perhaps we need to find other uses for them. One entertaining DIY science trick we can do is to melt part of the polycarbonate sheet and blow it out to create a giant bubble. Make sure to scrape off the aluminum sheet or else it won’t expand to its full amount. Enjoy!