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Overview:
Students compare and explain forces that act on air-filled and helium balloons. Students use both types of balloons to create a blimp that is neutrally buoyant and then modify their design with a propulsion system that will propel their blimp forward.

Objectives:

Materials:

• Aeronautic Engineer poster
• Pre-measured weights of paper clips

For each group (2-3 students)

• 2 9in balloons filled with helium
• Clear tape
• Duct tape
• Straws (not flexible)
• Large paper clips
• Small paper clips
• White copy paper
• Meter stick or tape.

For each student

• Build a Blimp Results page
• 1 - 9” balloon
• Parts of a Blimp diagram
• Engineer’s Journal

Vocabulary

Preparation:

• Conduct the activities prior to teaching the lesson. The blimp is constructed using two 9in balloons because one balloon will not float once the propulsion system is attached.
• Using Helium tank, per-fill 2 balloons/group before club.
• Students may inflate balloons by blowing into the straws, but they will need to switch out straws so that each student has their own to blow into.
• Make copies of Build a Blimp Results page.
• Make copies of Parts of a Blimp diagram.

Careers
Aerospace engineers create machines, from airplanes to spacecraft. They design, develop, and test aircraft, spacecraft, and missiles and supervise the manufacture of these products.  Aerospace engineers who work with aircraft are called aeronautical engineers.

Engage:

1. Hold up two balloons – one filled with air and one filled with helium. Let both balloons go. Ask students to explain the difference between the balloons. Answers might include - the balloon that floats is filled with helium gas. The balloon that sinks is filled with air.
2. Ask students if they think it is possible to design a system to make the balloons travel across the room instead of up or down. Ask and discuss:

• What special type of balloon can move horizontally? A blimp moves forward over the ground. The Goodyear blimp is a great example. They can be seen flying above stadiums during football games. Students will look at a diagram of a blimp later in the lesson.
• What are blimps used for? Blimps used to be used for military purposes. Today blimps are used for advertising, TV coverage, and tourism.

3. Before students begin brainstorming ways to make the balloons change direction they will need to understand how the two different balloons work. Ask and discuss:

• What force causes the air-filled balloon to sink? Gravity pulls on both balloons, but since the balloon filled with air is heavier than air by itself, it sinks to the ground.
• Why does the balloon filled with helium float? The helium gas is lighter than air.
• What other forces can cause a balloon to change its motion? Blowing wind and hitting a balloon can cause it to change motion.
• What would happen to the helium balloon if we went outside and released it? Students may share personal experiences of watching balloons float upward until gone from view. See background information for an example of a helium balloon that reaches the top of the atmosphere.
• How is the air like water? If you put an object such as a baseball in a pool, the ball will sink. If you put an empty bottle in a pool, the bottle will float at the top because the air filled bottle is lighter than the water. Compare the helium balloon to the bottle in the pool. The balloon will float toward the top of the atmosphere like the bottle will float to the top of the water.

Explore:

1. Introduce the challenge. Students will create a blimp that will travel forward across the room while displaying an advertisement. Students will need to control the forces acting on the blimp so that it will move forward.
2. Organize students into groups of two or three. Give each group two Mylar balloons, straws and clear tape. Ask and discuss:

• How can you connect the balloons so they move as one system? The lesson shows how to connect the balloons using one straw, but students may have other ideas they would like to try. Students must be careful not to add too much mass to the system. Otherwise the blimp will start to sink.
• How can you get the balloons to hover? Using the directions below, students will find that the blimp will still rise upward. They many suggest adding mass to help the balloon float in the air.

3. Groups follow their plan or the plan outlined below to connect their balloons and make the blimp hover.

Steps	Explain	Example
Students turn the Mylar balloons upside down and tape them to a straw so that one balloon sits behind the other. Students may use other methods of connecting balloons such as rolled up paper or skewers.	Turn the Mylar balloons upside down and tape them to a straw so that one balloon sits behind the other. Make sure the straw is taped securely to both balloons. This creates a frame for the blimp.
When students hold the straw, the balloons should sit next to each other.	One way to arrange the balloons is to position them behind one another. You can also place them side by side, but you will need to modify your straw so that it is long enough to connect the balloons.
Students will propel the blimp using a propulsion system made with a straw and latex balloon. Slip one end of the straw into the balloon. Tape the balloon to the straw using duct tape.	Your balloon needs a something to propel it forward. Ask and discuss: What are your ideas for propelling your blimp forward? Students share their ideas. You will use a straw and latex balloon for your propulsion system. Slip one end of the straw into the balloon. Tape the balloon to the straw using duct tape.
Tape the propulsion system to the bottom of the straw frame that connects the two Mylar balloons.	Tape the propulsion system to the bottom of the straw frame that connects the two Mylar balloons. Be sure to leave enough space at the open end of the straw so you can pump or blow air into the balloon.
If students let go of the blimp, it will probably rise into the air.  Provide students with large and small paper clips. Students will add paper clips until their blimp hovers. Students will know they are successful when the blimp hovers for at least five seconds before slowly sinking close to the floor or rising close to the ceiling. Even if the blimp eventually moves close to the ceiling or floor, it can still be considered as hovering.	If students let go, the balloons will probably rise into the air. Ask: What can you do to make your blimp hover like an actual blimp? Students should suggest adding weight. Demonstrate how they can unfold and hook paper clips to the frame. Add paper clips until your blimp hovers. You will know you are successful when the blimp hovers for at least five seconds.
Depending on drafts in the room, the blimp may float higher toward the ceiling or lower toward the ground. If it continues to float and stay at the ceiling, then students should add more paper clips. If it sinks to the ground and stays there, students should remove paper clips.	Depending on drafts in the room, the blimp may float higher toward the ceiling or lower toward the ground. If it floats to the ceiling, then you should add more paper clips. If it sinks to the ground and stays there, you should remove paper clips.
Students measure the mass of the paperclips.	Measure the mass of the paper clips when you have found the combination that allows your blimp to hover.

Explain:

1. Groups demonstrate their hovering blimps. Create a table on the board to record the mass required for each blimp to hover in the air.

• Why is the balloon able to float? Adding mass to the balloon makes it heavier. This allows gravity to pull the balloon toward the ground. Explain that the balloon is still buoyant, but it becomes neutrally buoyant when it neither sinks nor rises upward.
• What forces are being applied to the balloon? Gravity is pulling down on the balloon. The items attached to the balloon help to weigh it down.
• What propels a blimp? Give each students a Parts of a Blimp diagram. Read the article and discuss how the parts work together to provide thrust and lift for the blimp.
• What force could we apply to the balloon to make it move across the room? Students will explain that by filling the latex balloon with air and then letting go of the straw, the force of the air leaving the propulsion system will push the blimp forward. On the board, draw a diagram showing the force of air moving in one direction, and the motion of the blimp in the opposite direction.

2. Ask each group to inflate their balloons by blowing into the straw or using a balloon pump. Ask,

• When we let go of the straw, what should happen? Air will move out of the balloon and out through the straw. This force of air will push the balloon forward.

3. Ask each group to inflate their propulsion systems and then release them. Students discuss their results.

• Which way did the blimp travel? Why? Students explain the motion their blimp made. Many students will observe their balloons moving in a circular motion. Some balloons may move lower to the ground.
• What did the blimp do that you did not expect? Answers might include: The air we pushed into the balloon weighed the blimp down, making it sink to the floor.
• What might you want to change about the design so that it will travel in a straight line without sinking? Students will recognize that they need to remove some of the weight they added earlier so that the blimp will not sink after being released. Students may also suggest altering the design to make the blimp move in the desired direction.

Elaborate:

1. Remind students that their challenge is to control the forces acting on the blimp so that it can travel across the floor while displaying an advertisement.
2. Ask students to discuss in their groups the modifications they will need to make so their blimp will travel across the room to their partner. Students may refer the Parts of Blimp diagram for ideas. Students’ ideas may include:

• Adding tail fins: rudders and elevators
• Adding wings
• Changing the position of the balloons
• Making a new connection between the balloons
• Adding more balloon straws

3. Create a class list of modifications students may make based on each group’s discussion.
4. Students may cut fins, rudders, or other pieces out of white copy paper to help direct the blimp as it moves forward. Students need to keep in mind that any changes they make will affect the overall weight of the blimp. They must be sure not to weigh it down to the ground or let it float up to the ceiling.

5. Each group’s final touch will be to add an advertisement to their blimp.
6. Students test their blimp and make adjustments based on their results.

Evaluate:

1. Each group describes their design and demonstrates their blimp. Ask and discuss:

• How well did your propulsion system work? Did you have to make any changes? Answers will be based on results.
• How did you modify your blimp so that it could fly straight? Answers will be based on results.
• What would you still like to change in your design? Why? Answers will be based on results.

2. Students complete reflections in their Engineer’s Journal.
3. If time permits, ask students to consider what would happen if they connected all of the balloons. How much mass would they need to add to the super blimp to make it hover above the ground?

Resources:
How helium balloons work
http://science.howstuffworks.com/helium2.htm

How blimps work
http://science.howstuffworks.com/transport/flight/modern/blimp2.htm

Design Squad: Blimp Jet
http://pbskids.org/designsquad/pdf/parentseducators/DS_TG_BlimpJet_Teach.pdf

Sky Glider
http://pbskids.org/designsquad/parentseducators/resources/index.html?category=forceenergy

Background Information:

Helium balloons work because of buoyancy. Buoyancy is the ability of matter to float in a liquid or gas. Helium is a lot lighter than air, so a helium balloon that you hold by a string is floating in a "pool" of air and displacing an amount of air. As long as the helium plus the balloon is lighter than the air it displaces, the balloon will float. Helium weighs 0.1785 grams per liter. Nitrogen weighs 1.2506 grams per liter, and since nitrogen makes up about 80 percent of the air we breathe, 1.25 grams is a good approximation for the weight of a liter of air. A balloon that is one foot (30 centimeters) in diameter holds about half a cubic foot of helium, which is the same as 14 liters. This means the balloon will weigh about half an ounce (14 grams) less than the same sized balloon filled with air.

Because of its buoyancy the helium balloon floats upward. Blimps and balloons are generally quite large because they have to displace a lot of air to float.

If students are curious about how high a helium balloon will float in the air, here is an interesting experiment that films a helium balloon traveling to the top of the atmosphere before popping. http://blogs.howstuffworks.com/2010/10/22/when-i-let-a-balloon-go-how-high-can-it-go/

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___________________________
Girlstart is an award-winning Austin-based non-profit organization dedicated to empowering girls in science, technology, engineering, and math (STEM).

I understand that this is a funny headline for a science blog. But unfortunately we live in very politically volatile times. Although ideally science should be kept far, far, far away from the soap opera with a trillion dollar budget that is American politics, the reality is that politics and science are very much intertwined. Without the votes of our elected officials, there would be no funding for important and revolutionary projects like RHIC (Relativistic Heavy Ion Collider) at the Department of Energy's Brookhaven National Laboratory, a true modern marvel that I recently had the privilege to see. Totally funded by the United States government, this 2.5 mile circuit has the power to heat particles to up to four trillion degrees, and then smash them together to replicate conditions right after the Big Bang. Brookhaven scientists are working very hard in hopes of discovering vast new things about the origin of our universe.

Politics not only holds power over the current state of America’s scientific affairs, but also their future. For our government, local and national, has direct control over school curricula and funding. This means public officials have the power to graduate future scientists -- or not. If the schools stop taking science seriously, I can tell you for sure the students will stop too, if they haven’t already. This is precisely why it is crucial that scientists everywhere keep very close track of current political trends.

But above all else, this blog encourages rational thinking by exposing irrationality wherever it exists. Unfortunately the epicenter of irrationality often radiates from a white-domed, column-lined building, where every so often, 535 people congregate to determine the future of everything.

Last night, the United States House of Representatives passed HR 3590 with a vote of 219 to 212. This marks the greatest step forward in health care reform since the creation of Medicare and Medicaid. This bill will cover 32 million people who previously could not afford health insurance, ban discrimination based on pre-existing conditions, and prevent arbitrary rate hikes. The bi-partisan Congressional Budget Office conservatively estimates that this bill will save the United State over a trillion dollars.

It was a long and painful path from the moment President Obama announced his intentions to reform health care to last night's achievement. The national discussion was not a debate over critical data, economic realities and moral philosophy; it was a debate hijacked by a storm of irrationality. What should have been an open and honest discussion very quickly turned into the mass broadcasting of erroneous, fear-mongering rumors, with the other side's feeble attempts to dispel them falling on deaf ears. President Obama could have hung a giant banner outside the White House that read “HEALTH CARE REFORM WILL SAVE US $1 TRILLION!!!” And yet every time I turn on the television there is a Tea Partier or a Fox News anchor talking about how the bill will increase the national debt and drive up medical costs.

Dissent over health care reform is valid. But there is a difference between irrational dissent and rational dissent. When the opposition has to launch one of the largest disinformation campaigns ever perpetrated against the American populace, they invalidate themselves. One should never have to lie to prove a point. As a tragic result, half the population now thinks that a bill that is less progressive than what Republican governor Mitt Romney signed into law in Massachusetts, and far less progressive than systems that work for almost everyone living in Europe and Canada, will turn this country into the Soviet States of America, with a 90 percent tax hike on all the kids to pay for it. That’s not thinking scientifically.

A scientific thinker examines available data and forms a hypothesis. For the most part, the opposition to this bill tried to alter reality to fit the hypothesis they already created.

The fact that the Republican Party was almost successful in derailing this bill is not a sign of its strength but a sign of its decline. Not a single Republican in the house voted, not just for the bill, but even to debate it openly. When President Clinton proposed his plans for health care reform, there was unanimous consent to open debate. No bill in U.S. history has ever attracted this much partisan opposition to any bill. Even the 1964 Civil Rights Act had bi-partisan support. The Republicans have banded together to form one dogmatic, homogenous voting block against the Obama administration, no matter what its agenda may be. They have done so because they are desperate. The Republican Party is a cornered wolf, taking one ferocious last stand.

Firstly, let's take a look at minority voting trends. Statistically speaking, minorities tend to vote Democrat. According to population projections, it will not be long before minorities make up a majority of the American population. At a time when Republican survival depends on widening their tent, their new-found dogma has only managed to narrow it.

Secondly, the Republican base has been hijacked by former Alaska Republican governor Sarah Palin, the religious right, and the Tea Party. What this means is that rational Republicans have to distance themselves from the base of their party. They have to clarify that even though they are Republican, they are no fans of Palin or even former President George W. Bush. However, Republican candidates still have to campaign to their base if they stand a decent chance of winning primaries or drawing high turnouts for general elections.

Take Mitt Romney. He is a highly educated man who signed into Massachusetts law one of the most progressive pieces of health care legislation this country has seen. But when someone of his intellect goes on national television, as he did during the C-PAC conference, and calls Obama supporters “neo-liberal monarchs,” you know he knows better. Moderate Republicans and independents are forced to take a step back, and the Democrats now have another sound bite to use against Romney in 2012.

The third sign of the decline of the Republican Party is simply that America is growing more liberal. The majority of young people vote Democratic, support gay marriage and drug legalization, and are pro-choice. We also are the generation that didn’t grow up during the Cold War. Outside Tea Party and Wall Street culture, the Red Scare doesn’t really exist. The word "socialism" doesn’t send chills down our spines the way it did for our parents and grandparents. So we are more open minded when it comes to social programs, such as a public option.

These realities are forcing Republican strategists to use fear mongering and disinformation tactics to the point where their constituents are buying into a new reality, one that is not based on fact or reason. In this reality, even the U.S. Census, which has been constitutionally mandated since our nation's founding, has become unnecessarily controversial and called an “encroachment on our civil liberties.”

These tactics are most effective and most dangerous when they are implemented in our public schools. Some of our most important elections -- and often the most overlooked -- determine who serves on our school boards. Scientists especially should be paying very close attention to school board elections. All too often, a school’s science budget is the first line item to be cut, before sports. All too often, teaching widely accepted scientific theory is considered controversial. What goes into our curricula could easily determine the future of the scientific standing of the United States and how effective we will be in dealing with issues pertaining to the environment and energy independence.

There is no greater evidence of this than the recent conservative overhaul of Texas’ textbooks. In what came down to a party line vote, the overhaul went so far as to significantly downplay Thomas Jefferson’s role in history, simply because of his secular ideology and writings. What makes this even more frightening is that Texas is the largest buyer of textbooks in the nation. So textbook publishers must cater to the Texas curriculum to survive. Changes in Texas education affect the rest of the nation.

Grade school science is so much more than just teaching kids the periodic table or what happens when you mix vinegar and baking soda. Teaching the scientific method and habits of scientific thinking is crucial because it teaches kids to base their conclusions on data and observation. Students learn to have viewpoints that are reflective of reality -- not to have their reality reflect their viewpoints. To study the scientific method is to encourage rational thinking. When that is cut, then perhaps students will cease to question why Thomas Jefferson is no longer in their textbook.

Schools should encourage students to think scientifically and civically. What this country needs more than anything right now is a generation of young people who will grow up thinking that success is not determined by profit margin but by whether you make the world a better place for all. Last night, 219 men and women in Congress did just that. Because of the great risk they all took by voting for HR 3590, 32 million Americans finally got that breath of fresh air they so desperately needed. The passage of the health care bill will be remembered as one of the most important pieces of legislation since the Civil Rights Act and Medicare. The only thing that will prevent that is if we let the Republicans cut March 21, 2010 out of the textbooks.

Be Skeptical, Be Critical, Take Nothing On Faith.

All the best,

Jesse M. S.

If you live anywhere within continental United States, you are no doubt informed of the rippling snowstorm spreading across the country. Some citizens even experiencing snow for the first time, like many Texas residents who had the pleasure of receiving a whole foot of the stuff dumped on to their unsuspecting roads and houses. In Washington, DC, where I live the majority of the year, we experienced the worst snowstorm in 200 years. A storm powerful enough to shut down the roads, metro, schools and even the United States government for a whole week. A storm so intense, the district could not start plowing until four days in, making navigation and travel excruciatingly difficult. At American University, where I attend, not only were classes canceled for a week, but part of our dining hall collapsed. Luckily no one was hurt.

So from a crop freeze in Florida, to record high snowfalls across the country, to the crippling of our government, people, and by people I mean several conservative talk pundits and the sheep that blindly follow them, are starting to doubt climate change. Well not so much doubt, they’ve been doubting climate change ever since the airing of the first trailer of Inconvenient Truth. It is more accurate to say that they are delivering the rest of world, the demographic that is more in touch with reality, a very snowy and unwarranted “I told you so.”

At first glance, this is puzzling. Certainly an abrupt spike in weather phenomenon that is unprecedented in recent history bares some evidence that our climate is in fact changing. Scientists have stated over and over again that the shift in the Earth’s atmosphere will result in a higher frequency of storms that will become increasingly more severe. But unfortunately we made a colossal mistake. Just as our movement started to gain momentum beyond a few local farmers and recycling freaks, and evidence of our planets transformation began to take real form and reach broad consensus, Al Gore coined the term Global Warming.

Environmentalists have a lot to thank Al Gore for. An Inconvenient Truth rallied and educated millions of people and forced scientists and politicians to come out and address problems facing the environment. The film lifted the cause of a few commune living hippies and dismally funded lobby groups up onto its shoulders and into the national stage of conversation. In those respects, the film did its job flawlessly. Al Gore got people talking about the environment, and when people talk, they get interested and want to know more. Now the Environmental Protection Agency is operating on a budget larger than ever before, companies all over the world are spending millions of dollars investing in fuel-efficient cars and green technology. Mayor Bloomberg’s Plan NYC is going to plant a million new trees, sort through New York’s trash to find recyclables, require all schools to launch recycling programs and greenify building codes. Environmental Science is slowly becoming part of the core curriculum across the country. Environmental Filmmaking is now a major in universities everywhere. Even the set of 24 has gone green with digital scripts and carbon offsets.

A lot is being done, and the efforts of millions upon millions of people who are working as hard as they can to leave the Earth better than they found it are quite often overlooked. However, as much as we are indebted to Al Gore for legitimizing our movement, he also made a crucial mistake. You see Al Gore is a democrat and unfortunately being a democrat he is cursed with the inability to name things well. Lets look at some of the names Republicans have come up with, The Patriot Act, a law that limited civil liberties. The Internet Freedom Act, a bill that would allow companies to control the speed and content of the Internet based on how much you pay them. The Pro Life movement has a great name, hell, even the Tea Party is kind of cleverly dubbed in its own way.

Democrats have Cap and Trade, Gas Tax, and Single Payer Healthcare System to name a few. Doesn’t have quite the same ring. Al Gore decided to call the shift in Earth’s climate global warming. And although there is legitimacy in that name. Sunlight is being trapped in the Earth’s atmosphere by fossil fuels, which are heating it up. But that doesn’t necessarily mean the weather we experience on the ground is warmer. In fact a melting ice cap will result in colder ocean temperatures. And even though the last two winters were some of the warmest on record, the fact that global warming and not climate change is the common terminology, every time Sean Hannity has to ware a coat to get to work he can later go on TV and call Al Gore’s theory “hysterical.” The frightening thing about that is people believe him, a lot of people, and now every time the weather is colder than usual or snow falls in areas where it shouldn’t be falling, the entire green movement is undermined.

The environmental movement is asking for our civilization to sacrifice a lot. The way we get around, the way we eat, our entertainment, one could say a whole culture is being called into question. We sometimes forget the scope of what we demand from our fellow citizens to save this Earth. That is why there really is no room for error. We cannot afford to have our statements taken out of context, we cannot afford to be dishonest, and we have to always remember the more disorganized we look, the more we falter, the less legitimized we appear to be and the less people are willing to take us seriously and perform the sacrifices the world desperately needs them to do.

Be Skeptical, Be Critical, Take Nothing On Faith.

All the best,
Jesse M. S.

No one likes taking tests. Unless you are really well prepared and know the answers to all of the questions. And then it can be fun as an affirmation of your hard work, perseverance, and mastery of the material.

My first big, important, life-changing test occurred in the 8th grade. The DATs—tests to help you figure out what career you might be good at. Don’t remember what the “D” stood for. On this 6 part test, I scored in the 99th percentile in spatial relationships, mechanical thinking, scientific reasoning and mathematical concepts. But I only scored 80th percentile on transcription and memorization. When the test results came out, the guidance counselor met with my parents to tell them what line of work I would best be suited for.

Based on my scores, my counselor told my father I would be a very good secretary! To his credit, my father told the counselor that his honor student daughter could be other things beyond a secretary. And then he told me to ignore her the same way she ignored those tests.

Why do I tell you this? Because tests, while important in helping someone else determine your strengths and weaknesses, are only one part of what you are and what you are going to become. They are simply not a complete picture of you.

Having said that, it is important to know that test taking is a fact of life if you are going to become a doctor. The tests start early and they seem to never end. In fact, every time you take on the care of a patient, in some way, you are being tested as to how good you are as a doctor.

But let’s leave that particular philosophical debate aside for the moment. Practically speaking: What kind of tests will you encounter? How important are they in becoming a doctor? When do you take your last test?

First, it is very important you know how to take tests. The subject matter is important, and preparation is the key to success. There are the tests you take for classes. Teachers are usually pretty generous in letting you know what to study. But then there are those dreaded standardized tests that colleges require for your application to their school. Unfortunately, many times these tests are used as cut offs to separate out students who will be considered for admission and those who won’t.

The last time I looked, the pre-SATs (scholastic aptitude tests) are taken early in the junior year of high school. These tests help determine who will receive national merit scholarships. They also give the student a taste for what’s to come.

Then comes the big sister test. The SATs. They have three parts—math, English and writing sample. These scores are weighted more or less heavily towards admission depending on the college. Their results are also provided to colleges which then begin the process of sending you material encouraging you to apply to their school.

Prep courses abound. Is Kaplan better than Princeton Review? Don’t know. But they can be expensive, and I do not think there is financial aid for the near $1000 fee charged for college preparatory tests. (I sent an inquiry to each last month, but have yet to receive and answer). But they also can help boost your scores and even guarantee it or your money back.

Even without test prep courses, you can find used test prep books on-line. And then: Practice. Practice. Practice. The discipline is not only useful for these first tests, but also will help you learn how to learn to take tests for the rest of your life. Alas, a painfully necessary skill.

Hey, Dana, now that you are back from the Big Sur, what do you think of my take on tests?

So while Dana is off with younger sister Becca exploring the beauty of Big Sur, CA, during their winter break, I will tackle the first of the many great questions Rosie asked.

“How long is it to the step where you can finally say that you are a doctor?” Hard question. The answer starts with “it depends.” When is someone really a doctor?

Becoming a doctor is a process. A long process, which doesn’t really ever end until you stop caring for patients.

It can begin in high school, college or even later on. There is no one route to get there. But for the purposes of answering this one question, let’s look at the straight and narrow path to becoming a doctor.

Start with graduating high school. Take challenging courses. Get good grades. Learn to study and take tests. Find other interests. Take care of yourself and the important relationships in life. Takes about 4 years.

Go to college. The best one for you. Sometimes people don’t want to leave their family to go to a “top-rated” school or they don’t have the money, or the grades. Don’t let that stop you! Find the best fit and do your very best. Find your academic interests (may not be science, but you still have your pre-meds). Take challenging courses. Get good grades. Learn to study and to write well. Learn to take tests. Build on your outside interests. And take good care of yourself, your family and your friends. (College is usually four years, but there are some programs which combine college and medical school in 6 years.)

Go to medical school. There is no one “best” school. Medical school is almost always 4 years in length, unless you pursue a PhD in the biological sciences or, more often now, in the social sciences (like Dana who is also getting a PhD in medical anthropology).

At the end of medical school you are allowed to call yourself a doctor. The title of MD (medical doctor) or DO (doctor of osteopathy) is appended to your name. Does that make you a doctor? Well, it depends on what you want to do.

If you want to go into related fields where an MD or DO is helpful and your primary job is not one-on-one patient contact, then you have become a doctor. One of my medical school classmates works in research designing clinical trials. He never “touches” a patient but his valuable work truly touches the lives of many patients by providing information helpful to thousands of people.

But if you are like most people who travel the first 12 years, you want to take care of patients. How long? It depends on your field of medicine.

The day I graduated medical school, Dr. David Wagner, pediatric surgeon and director of emergency medicine, “hooded” our class. As I accepted the white fur cowl bestowed on one who earns the MD degree, he said to me, “You will live, eat and breathe medicine for the next 5 years. Learn everything you can about diseases and everything you can about the people who will suffer from those diseases.” Great advice that I took very much to heart.

Now you become a resident. You make the most of every patient encounter. You learn all kinds of skills, study hard and work long hours. The patients become your teachers while you are closely supervised by more experienced doctors.

Your formal training is over. It is 3 or 5 or sometimes even 9 years later. You can finally go out into the world and show people that you have learned and earned what it takes to be called a doctor, a healer. Sound daunting. It is. But it goes very fast. Be propelled by how exciting and important your life’s work is to you and for everyone who will help.

Therefore, my next topic will be another argument for the existence of dark matter, and in my opinion one of the cooler phenomena in physics (I understand that my stating something is "cool" is not necessarily sufficient evidence, but I will try to explain) - the Cosmic Microwave Background or CMB for short (another good name, by the way).

In very broad strokes, the CMB is an echo or an image of the universe as it was 13 billion years ago (when it was only four hundred thousand years old - relative to the human lifespan, it's like we have a baby picture from when the universe was 1 day old). Much as archaeologists can learn about prehistoric epochs from fossils (or mosquitos trapped in amber) and geologists can infer the climate from ice cores that have been frozen for thousands of years, physicists can discover information about the contemporary contents and future evolution of the universe by studying the CMB.

So what is the CMB? It's a sea of light streaming across the universe in all directions that was produced 13 billion years ago and has not touched anything since that time. This light isn't visible to us, because its wavelength (remember these posts) is in the microwave band (i.e. too long to be visible by our eyes, but with enough intensity [thankfully not present in the actual CMB or else we'd all be in trouble], perfect for heating up instant hot chocolate [too quaint?]). It's always there though, and like a photograph, each individual photon contains an image of the universe shortly after the big bang.

The illustration (click for a bigger view) shows the history of the universe from the Big Bang to the present. The CMB is produced at the green and blue ellipse during the very early universe and detected in the present by the satellite labeled "WMAP."

I'll stop there for now, but hopefully the reader will want to know more. I'll probably refer to two web sites a great deal in the coming posts. The best existing CMB experiment is the Wilkinson Microwave Anisotropy Probe, or WMAP, and they have a great resource at http://map.gsfc.nasa.gov/ from which I've taken the illustration. The second web site is where I learned most of what I'll be talking about, the homepage of Professor Wayne Hu of the University of Chicago. He's done a great job explaining all the details and implications of the CMB in simple terms, and I hope to do half as good a job.

I know in my last post I expounded following one’s own interests, without any particular roadmap. This approach definitely has its positives. But sometimes confusion and uncertainty appear, and choices can be difficult to make. Solution? Mentors as my guideposts: While I may not be sure what might lay ahead, for the immediate future, they have helped me to know that at least I was in the right place.

Times have changed. And so have the kinds of advice and guidance that young people need. Maybe back in the 50s and 60s when you (mom) were growing up, mentorship of young women was up against much more narrow and stifling gender stereotypes. Mentors were needed to open the door, make more things possible for more girls.

For me, mentorship has served a very different function. I grew up in very different circumstances. The 80s and 90s were more liberated times. I was raised by two surgeons, and never were we allowed to believe that less was expected of girl. But even with such strong role models that didn’t mean that I didn’t need help.

Today’s world is so much more complex. The opportunities may have exploded, but learning to navigate these opportunities has never been more difficult.

Mom, you needed permission to pursue your dreams. I needed focus. My life was and still is marked by too many overwhelming possibilities. And my mentors have always been there to refocus my limitless vision.

I have so many questions that can have so many answers: What kind of doctor do I want to be? Where do I want to practice? What kind of anthropology do I want to do? Where should I do my fieldwork? How does it all fit together into a nice neat package of a career?

Even the more immediate, smaller concerns gnaw at me: Which clinical rotations should I do this summer? Am I doing enough reading, writing, research, extra-curriculars, etc? When should I start studying for the board exams? How do I compare to every other second year med student?

My advisors at Barnard, my research mentors all over the world, the many physicians and researchers who teach me at UCSF everyday, and, of course, my family have all done (and do) two crucial things: 1. they gave me a chance at my dreams and 2. they helped me stay on track amidst all the chaos and uncertainty.

My meetings with my PhD advisor: I am worried what I’ll write my dissertation on, how I’ll pick a topic, a place or a community, or how I compare to my more entrepreneurial and innovative colleagues. With a knowing smile she reminds me of my strengths, my ideas, and gently nudges me to stay on track and keep my eyes, ears, and mind open all at the same time. And bam! I’m a new person and life makes sense again.

I guess it doesn’t seem so impressive on paper, but these sorts of interactions have an intangible magic all of their own.

Maybe it’s just me. Or perhaps I’m too insecure or just too willing to admit it. But I need these guideposts at regular intervals, checking in along my way.

So if, like me, you’re prone to flurries of ideas, abundant curiosity and a little (well, ok, a lot) of angst, look for mentors who can help you harness the energy of uncertainty to take you in positive, yet uncharted directions.

We know the equation of circular motion, F=mv²/r. And by hypothesis, the only force acting on the object in orbit is the force of gravity, F=G*m₁*m₂/r². In this case, m₁ is the mass of the galaxy, and m₂ is the mass of the object. We equate the forces, so mv2/r = G*m₁*m₂/r². Now, the mass from the circular motion equation is just the mass of the object in orbit, so m₂ will cancel. All that remains is to solve for the velocity, since that's what we measure using the Doppler effect and red shift.

m₂*v²/r = G*m₁*m₂/r²

First, divide both sides by m₂

v²/r = G*m₁/r²

Next, multiply through by r

v² = G*m₁/r

Now, take the square root of both sides

v = Sqrt(G*m₁/r)

And that's it. We have derived that the velocity of an object in orbit about a galaxy should be proportional to the square root of the mass of the galaxy divided by the orbital radius. There is one more thing we should be aware of, which is that I haven't made any assumptions yet about the size of the mass of the galaxy. A galaxy is a very large thing, and what happens if you're inside part of it? For example, the Sun and the Earth are somewhere inside the Milky Way galaxy. We do orbit the Milky Way center, but part of the Milky Way is outside our orbit. The answer is that in this case, m₁ refers the total mass inside the orbit. It doesn't matter how spatially extended it is in space, as long as the object in which we're interested is outside of the galaxy, the equations are fine. And since I'm particularly interested in the mass of the bright part of the galaxy, it's easy to know when we're outside that part, so everything holds.

Now, let's look at a plot. If all the mass were in the bright part of the galaxy, then outside the bright part (say a radius of 100, just to make the plot look right), from the last equation, we would expect the velocity to fall like 1/Sqrt(r) (G and m₁ would be constant). That would look like this:

Instead, we measure a flat line, like this:

Therefore, by deduction, we know that either Newtonian gravity is wrong (a possibility, I'll admit), or that there is more mass than we thought, mass that is not contained in the bright part of the galaxy. In fact, we know the distribution of that mass, as it has to increase like 1/Sqrt(r) or else the the velocity would not be flat.

This is what some of the actual data looks like:

These are measurements of galaxy rotation curves (Begeman, Broeils and Sanders, Mon. Not. R. astr. Soc., 1991, 249, 523). I apologize for the image quality, but velocity is on the y-axis and radius is on the x-axis, and all the black points are actual measurements. You can see at small radius the velocity increases. This is where the bright part of the galaxy is, and as the radius increases, we are containing more mass in the orbit. At larger radius, we would expect to see the velocity drop. But instead, it stays constant. The dashed and dotted lines are the the components of the mass, the bright part and the dark part. This data provides evidence that there is matter that we are not seeing, that is not interacting with light, but is dark matter.

In the first part of the book, in order to draw parallels with current scientific evidence for the “epidemics of obesity and diabetes,” he puts forth a detailed historical analysis of the decades-long debate on the correlation, or causation, of heart disease with dietary fat intake. The upshot of this work is to point out what happens when a researcher, who becomes prominent for various reasons, can influence health care policy even when the researcher’s scientific data are far from conclusive. In this particular case, Taubes discusses the work of the prominent physiologist Ancel Keys, who was convinced, based on his research that the rise in incidence of heart disease in the developed world from the 1920s through the 1950s was due to increased blood cholesterol levels, which was in turn due to increased total dietary fat intake. Keys was apparently a formidable character who felt very strongly that his data conclusively proved this hypothesis, and was very quick to strongly criticize those who opposed his theories. Throughout this time period, and even into the 1960s, there were many prominent researchers who had serious reservations, based on scientific analysis of his data as well as their own, that Keys’ results were inconclusive. Nevertheless, because Keys was so forceful, Taubes brings various elements to show that the media picked up Keys’ theories, and physicians began to recommend low fat diets to their patients, despite lack of strong scientific evidence for increased dietary cholesterol intake (mainly from animal fats) causing a rise in heart disease.

In such a scenario, the question becomes one of correlation versus causation, i.e., depending on how solid the scientific evidence is for any given observed public health phenomenon, one might be able to say there is a CORRELATION of a dietary trend with observed disease incidence, rather than being able to state, through a solid base of scientific evidence, that a given dietary trend CAUSES disease. This concept is one that the Health at Every Size paradigm considers regarding current dietary habits with the incidence of “obesity” and diabetes. The bottom line is that there is still much scientific work that needs to be done to determine whether lifestyle in the developed world causes, versus merely correlates with, “obesity” and diabetes.

One reason for this phenomenon of correlation overpowering the media is that it provides a solid message to address what appears to be an alarming trend. Understandably, people don’t have the patience to wait for conclusive scientific evidence to be produced when faced with a potentially scary scenario. When scientific evidence that contradicts the popular theory is published, it tends to be ignored, because it doesn’t fit what has become DOGMA, based on the popular correlation. Taubes skillfully points out that when correlations are not thoroughly researched scientifically, and they become socially accepted dogma, real scientific progress just breaks down. Ultimately, I believe, the truth always emerges in the end, and the road of public health history is littered with the corpses of what used to be very popular theories. But while the dogma exists, well meaning but misguided health professionals may in fact do more harm than good, by encouraging unrealistic weight loss goals rather than focus on lifestyle changes.