How Much Water Fits On a Penny?

Materials:

• penny
• eyedropper or pipette (if you don't have one this article explains how to make one)
• water
• other liquids
• soap

Make a chart like this (or feel free to copy this one and print it):

Liquid	Predicted # of drops	Actual # of drops
1.
2.
3.
4.
5.
6.
7.

My supplies

For each liquid, you are going to use your eyedropper to carefully drop the liquid onto the penny until it spills over. Record the number of drops that fit. Try and make a prediction before you do it each time.

You can use any and all liquids you want (assuming they are non-toxic obviously). However, make sure you try this with both normal tap water and soapy water. And be sure to wash and dry your penny between each new liquid (and rinse off your dropping device as well).

What's Happening?

The atoms/molecules in a substance are all attracted to each other through intermolecular forces (IMFs). This can be because the molecules are polar (meaning one side is slightly more positive than the other) such as with water. Or it can be because the molecules are big enough that the electrons moving around can induce positive and negative poles. Whatever the reason, when the IMF is between molecules in the same substance, it is called cohesion. So all the molecules on the inside of the liquid are attracted to all the molecules around them. However the molecules on the surface of the liquid don't have any molecules above them to be attracted to, so they are more attracted to the molecules on the inside. This forms a "film" on the surface and keeps the liquid together in a drop.

Since water is polar, and therefore has high IMFs, its surface tension is relatively high. So more water should be able to fit on the penny before the surface film "breaks" and the water spills everywhere.

Image courtesy of factfixx.com

Here's my data chart:

Liquid	# of drops
1.       Water	24
2.       Water	26
3.       Soapy water	23
4.       Milk	22
5.       Salt water	14

Huh... not what I expected at all! Except for the salt water, the number of drops is pretty similar in each. So either the explanation I just gave was wrong, or something happened in the experiment that I didn't account for. Even though the number of drops was the same, I definitely felt suspicious because the blob of soapy water on the penny just didn't look as big as the one from normal water had been. I also felt like the size of the drops were smaller. So since I was using a syringe with volume measurements marked on the side, I filled the syringe up to 1 mL each time and after I had finished dropping on the penny, I continued counting drops until I had emptied the syringe.

So here's my new data table:

Liquid	# of drops	# drops in 1 mL	Ratio
1.       Water	24	23	1.0
2.       Water	26	19	1.4
3.       Soapy water	23	46	0.50
4.       Milk	22	27	0.81
5.       Salt water	14	22	0.64

Now the results make a little more sense. And it does make sense that the drops would be smaller - they have less surface tension to hold them together. I find it interesting though that none of the websites that reminded me of this activity (this isn't the first time I've done this, I actually distinctly remember doing the penny water drops experiment in 3rd grade) mentioned this fact. It might have just been the syringe I used. If anyone else tries this, I'd be interested in hearing how it worked out.

Learn more:
http://hyperphysics.phy-astr.gsu.edu/hbase/surten.html#c4
http://www.chem.purdue.edu/gchelp/liquids/tension.html 

Khan Academy

Topics: Math, Science, Economics, Computer Science, Humanities
Explanation Quality: Better
Medium: Video, Practice Problems
Type of Content: Teaching Material

Many of you have probably already heard of Khan Academy. It is a website offering short videos and practice problems in a variety of subjects. It was originally created to help the creator tutor his cousin over the internet. The videos feature someone (in many it is the founder Sal) giving a short (under 20 minute) explanation while writing it out on the video screen.

There are videos in economics, math, history, and the sciences. There are only practice problems in chemistry and math, but the difficulty ranges from telling time to calculus. I find the practice problems very helpful. The videos are good too. He attempts to explain each thing in several ways, and does examples in the videos. I have one minor problem with them: I often watch videos to review something from class or to compile all the bits I have learned from different sources. So parts of the video are new things/things I didn't understand, and parts I already know. I end up not wanting to watch the parts I already understand, but I don't want to skip forward in case he mentions something else new. But as I said, this isn't really a big problem.

If you make an account, watching videos and doing problems earns you points and achievements which is a fun additional motivator. They also show stats of how much you have been working on skills or watching videos. Personally, I love things that chart my progress.

If you are a parent/teacher/helpful older sibling, you can monitor your child/student/younger sibling's progress. I have my little sister's account registered as a child account under mine so I can make sure she is still doing work over the summer. When I see that she hasn't done her tasks for the day (she is supposed to learn one skill of her choosing every day to make sure she is doing something educational with her time) I can then react appropriately. But don't worry, you don't need a coach or mentor to use this site. It is good for anyone who wants to learn something.

Brilliant

Topics: Math, Physics, Computer Science
Explanation Quality: Good
Medium: Problems, Text
Type of Content: Recreational, Practice Problems

Brilliant.org is one of my favorite math websites. It offers a a new set of problems every week in a variety of topics. Before you start doing problems in a certain topic, you do a few problems to determine your level. The site then places  you appropriately and you can get started with this week's problem set. You level up if you consistently do well.

What I like about it is that the problems are interesting. You don't immediately know how to go about solving something. I always end up with a few problems I can't figure out. At the end of the week, you can view solutions to all the problems. You can also offer your own solutions and help out others who didn't get it.

While the main section of the site has olympiad type problems, there is also a practice section where you can choose to work on specific techniques. It is helpful for reviewing topics from school. It also actually explains methods of solving the problems, instead of just throwing you in there. I personally don't use that section as much, because I have more fun with the main problem sets. There are also smaller weekly problem sets in physics and computer science. I expect the sections to expand in the near future but for now the bulk of the site is math.

So head on over and have some fun!

S'mores at the Speed of Light

Materials:

• Chocolate
• Marshmallows
• Microwave (you will need to know the frequency. If you can't find it the norm is 2.45 GHz)
• Ruler
• Something to do calculations on
• Graham Crackers

 First, if your microwave has a rotating dish in the center, you will need to remove it. Or figure out some way to put food in so it won't rotate. Then lay your bar of chocolate (open it first!) on a plate to place it in the microwave in such a way that it won't rotate.

The red circles are the melted spots.

Image courtesy of Null Hypothesis

Microwave it for a bit, until there are 2 melted patches. 20 seconds should work. Now remove it from the microwave and use your ruler to measure between the two melted spots. Spread the marshmallows out on a plate and repeat.

Sci Show

Topics: General Science
Explanation Quality: Best
Medium: Video
Type of Content: News, Teaching
 
SciShow is a youtube channel run by Hank Green. It posts several different types of videos. There is a weekly video with science news. There are shorter videos on a variety of interesting topics - my favorite is on Non-Newtonian fluids. These offer a quick overview of something.

There are also longer videos which offer more information. My favorite one of those is on epigenetics. Basically, this channel is a good place to learn a bit about a random topic. If you have something specific you want to know about in mind this might not be the right place, but if you just want to keep updated on what's happening in the world, or don't care what you learn about, then this is the place for you. This is not to say that SciShow won't help you if you are trying to learn about a specific topic. I was able to use one of their videos in a presentation on radiation.

The videos are always easily understandable, and normally humorous as well. So go check it out!

Plans for the Future

I apologize for not updating frequently. Normally what happens when I want to write a post, I find a topic or experiment that looks cool. If it's an experiment I write up how to do it. Then I research. A lot. It takes me a while to have learned enough about a topic to be able to write an understandable explanation of a topic. Especially because it is very difficult to find understandable information on complex topics. I am going to make an effort to post stuff more regularly.

Since there is a lot of science on the internet and there is no way I will be able to explain as much as I want to, I am going to start posting some of my favorite sites when I go to start learning about a new topic. I often get frustrated by constantly finding information that is too basic or is much too complex, but these sites normally help. In addition, I made a science board on Pinterest! There I will post bite-size experiments and fun facts. The explanations won't be as in-depth as they are here, but it's something fun I want to try.

I also want to try and add more pictures to my posts. I feel they can aid in explaining complicated concepts, or in helping to understand directions for an experiment. So if you find an old post suddenly has a picture when you swear it didn't before, don't be alarmed. You're not going crazy, I'm just updating it.

Plasma

I wanted to learn more about "weird" states of matter the other day, so I decided to start by researching plasma. I was shocked when I found out that plasma is THE most common naturally occurring state of matter in the universe. It is estimated to compose 99% of visible matter. And yet, in school I have learned virtually nothing about it. I heard about it only from when a teacher would ask "What are the 3 states of matter?" and some kid would answer plasma. The teacher would say "Well technically yes, but we're not going to talk about it now." And this has been happening for years.So here is an overview that hopefully helps your understanding.

Plasma is an ionized gas. A gas is a collection of atoms and/or molecules floating around freely. It is a fluid, meaning it flows like a liquid. It is also very compressible. A gas becomes a plasma after being subjected to either high temperatures or other energy. This causes the molecules (or atoms, but for the rest of this post I'm just going to say molecules and just assume I mean whatever type of particle the gas is composed of) to ionize.

Ionizing a molecule means either adding electrons or ripping them off. In this case, it usually means ripping them off. So the plasma is composed of the ions and the electrons that have been removed. Not all the molecules have to be ionized though. There can be varying ratios of ions to molecules. This ratio is called the degree of ionization. Plasmas are (usually) quasi-neutral, meaning they have approximately equal amounts of positive and negative charges.

Plasmas can be thermal or non-thermal. If it is thermal, that means the ions, neutral particles, and electrons are in thermal equilibrium. In other words, all the particles are roughly the same temperature. In a non-thermal plasma, ions and neutral particles will be the same temperature (normally close to that of the surroundings) while the electrons will be MUCH hotter.

Examples of plasma in everyday life include lightning, neon lights, and the sun. Although flames are present on this chart, there is some controversy over whether they are actually a plasma. The majority says no, and even if fire is plasma, it is a very weakly ionized one that doesn't show all of the properties. There has also been some work done in cooling non-neutral plasmas (plasmas composed entirely of one type of charged particle) done to temperatures within a few milli-Kelvins of absolute zero. In these instances the plasma forms a crystal lattice structure.

This is only a brief overview. It was very difficult to find information that was both trustworthy and at a level I could understand, so if there are any errors please notify me immediately (with sources).

To learn more, check out these links:
http://science.energy.gov/~/media/fes/pdf/about/Low_temp_plasma_report_march_2008.pdf
http://sdphca.ucsd.edu/index.html
http://www.plasmacoalition.org/edu.htm   (this one is actually a page full of more resources)