Friction: Friend or Foe?

By Penubag (Own work) [Public domain], via Wikimedia Commons

We've been learning about forces this semester. Often, we treat surfaces as "frictionless" to simplify calculations. When we talk about machines, we sometimes "neglect friction" and assume the machines are ideal. By doing these things, it's easy to associate friction with something bad. It is true that there are many situations where friction is not desired, and engineers usually take steps to reduce friction in their designs.

However, that's not the whole story. Sometimes friction in desired. What examples or applications can you think of where friction is "the good guy"? Post your ideas in the comments section.

Photo from Mars

An amazing self-portrait has just been taken on Mars. Here are a few questions to get us started this marking period:

1. What is this a picture of?
2. What is the purpose of this vehicle's mission?
3. What do you hope or think scientists will learn as a result?

News from Space!

Artist's rendition of the newly-discovered planet orbiting nearby Alpha Centauri. (Photo used with permission from ESO/L. Calçada/Nick Risinger.)

This week, there are several popular news stories involving space. First, there was Felix Baumgartner's daring skydive from the edge of space. Then, on Wednesday, thousands of Californians witnessed a very bright meteor (thought to be a remnant of Halley's Comet). Finally, astronomers announced the discovery of an Earth-sized planet orbiting the Sun's next door neighbor, Alpha Centauri.

This has been an interesting week in astronomy! Answer some or all of the questions in the comments section.

1. Which of these news stories is most exciting to you? Why do you feel that way?
2. Does Baumgartner's jump make him the fastest human to ever travel through the air without being enclosed in a vehicle? Explain.
3. Halley's Comet orbits the Sun once every 76 years. How often does the earth travel through the remnants of Halley's Comet?
4. Alpha Centauri is quite different from the Sun because it is a binary system--there are actually two (or three if Proxima Centauri is included) stars gravitationally bound to each other. How would these two stars appear from the surface of the newly-discovered planet? Would they look like twin suns?

Another Look at Free Fall

Photo used with permission under Creative Commons license from Dennis Jarvis.

We've been studying free fall in physics. We have often made use of the idea of symmetry in our calculations to greatly simplify problems. For example, one of the questions on our recent test was:

Suppose a cannonball is fired vertically from ground-height at an initial velocity of 30 m/s. How long is the cannonball in flight before it crashes back to the ground? (Assume no air resistance in this problem.)

The easy way to do this problem is calculate how long the cannonball takes to get to the peak of its trajectory:

v_f  =  v_i + a*t

0 = 30 + (-9.8) * t

t = 3.06 seconds

Since, by our symmetry argument, the cannonball spends an equal time going down as it does going up, we can double our result to find the overall time:

total time = 2 * (time going up)

total time = 2 * 3.06

total time = 6.12 seconds

While this is a quick and easy way to calculate the answer, does it make assumptions that are not true? Is the symmetry argument really valid in this case? Is there a way to determine the answer of 6.12 seconds of total flight time without using the symmetry argument?

In the comments, explain how it is possible to get t = 6.12 seconds without using the symmetry argument. What equations would you use and how do they work out?

Arduino Toggling Fun!

Photo used through Creative Commons License by Snootlab.

Students in Honors Physics II will appreciate the helpful code shown below--it allows a single push-button switch to toggle an LED on and off (just copy and paste it into the Arduino IDE). Even if you're not a programmer, can you figure out the main idea of each line of code?


/*
Brian Bearss
10/1/2012

Button Experiment!

*/

int ledPin = 12; // connect a LED (and a current-limiting resistor) to pin 12
int inputPin = 7; // a push-button switch is connected here
int newState = 0; // a variable to keep track of the current position of the button
int oldState = 0; // a variable to keep track of the position of the button the last time through the loop
int ledState = 0; // a variable to keep track of the state of the LED (on or off)


void setup()
{
  pinMode(ledPin,OUTPUT);
  pinMode(inputPin,INPUT);
  //Serial.begin(9600);
}

void loop()
{
  newState = digitalRead(inputPin); // will be HIGH when button is depressed, LOW otherwise
  if(newState==HIGH)
  {
    if(oldState==LOW) // this means the button has "just" been pressed
    {
      if(ledState==LOW) // this applies when the LED was previously off
      {
        digitalWrite(ledPin,HIGH); //turn the LED on
        ledState=HIGH; // record that the LED is now on
      }
      else // this applies when the LED wsa previously on
      {
        digitalWrite(ledPin,LOW); // turn the LED off
        ledState=LOW; // record that the LED is now off
      }
    }
  }
    oldState=newState; // update the state of the button so we can tell when it has been pressed
    //Serial.println(newState);
    delay(10); // wait 10 ms to allow the pysical button to stabilize before repeating the loop
    
}

A Basketball in Free Fall

A screenshot of our motion graphs.

We've been studying motion this week in class. We used an iOS app called Vernier Video Physics ($2.99 on the App Store) to analyze the motion of a basketball. Specifically, we tossed a basketball straight up into the air. The top graph shows vertical position vs. time, and the bottom graph shows the basketball's vertical velocity vs. time.

In the comments, answer one of the following questions (just one so other students will have a chance too):

1. How high above the ground was the basketball when it was first thrown?
2. Estimate the highest height attained by the basketball.
3. With what speed was the basketball initially launched (when it first left the student's hand)?
4. How long was the basketball in flight before it reached the apex of its trip?
5. In class, we calculated the slope of the bottom graph to be about 8.8. What are the correct units for this slope?

Finally, let's get lots of comments on this question:

1. The acceleration of gravity near the Earth's surface is known to be 9.8 m/s/s which is a little higher than the acceleration measured by our experiment. Why does it make sense that our particular basketball's acceleration was a little lower than ideally expected?

Welcome Back!

Photo by riekhavoc used with permission through Creative Commons.

Welcome to a new school year! As this is the first blog post of the school year, I'd like to keep it very short and very simple. Post a comment to one or both of the following questions:

1. What would you like to learn this year in physics? Are there any topics in which you're especially interested?
2. What are your academic goals this year?

I am eager to read what you think.

Transit of Venus

Photo by Jan Herold

Venus will be transiting the Sun today (June 5, 2012). This astronomical event is fairly rare. In fact, today is only the seventh time Venus has transited the Sun since the telescope was invented. In addition to being a once-in-a-lifetime event, the transit will allow astronomers the opportunity to capture some valuable data and make important observations. Do a little research about what astronomers hope to learn from today's transit.

• What research questions will astronomers be pursuing during the transit?
• Why can some of this data only be obtained during a transit?
• How is a transit related to an eclipse?

Post your answers to these questions, and feel free to comment on previous comments as well.

The Proof of Innocence

Photo by Tripp.

Recently, Dmitri Krioukov, a senior research scientist at University of California - San Diego, was issued a traffic citation for failing to stop at a stop sign. Krioukov claims that he did, in fact, stop, and that the officer made a mistake in assuming that he did not.

Rather than pay the $400 fine, Krioukov decided to put his skills to use and wrote a paper explaining his theory. The four-page paper, titled "The Proof of Innocence" is posted online. 

1. Krioukov claims that his car might have appeared to have not stopped at the stop sign, proved three conditions are true. What are these three conditions?
2. Krioukov frequently uses the term "angular speed." What does he mean by this, and how is it related to linear speed?
3. News articles about the issue have been posted by the Los Angeles Times and (a different version) by Fox News. Read about the situation and comment on whether or not, in your opinion, Krioukov  should have to pay the $400 fine.

Pulleys Everywhere?

Photo by emkladil.

We've been studying simple machines in class, and we've talked about lots of examples of each type. In this post, I'd like us to focus specifically on pulleys:

1. Sometimes, a pulley simply changes the direction of a force without increasing the force. Therefore, the mechanical advantage (MA) is 1. Other times, pulleys can be used to increase a force (and have mechanical advantage of much greater than 1). How can this be? How can you tell just by looking at the pulley whether or not it will increase the applied force?
2. Where are pulleys used in practical applications?
3. Look carefully at the pulley in the photo at the top of the page. How might this pulley be used?

Physics Pays?

A team of physicists hope to set off a controlled nuclear fusion reaction at Lawrence Livermore National Labs  in Livermore, California. Photo by Steve Jurvetson.

I recently stumbled upon an article written at Payscale.com examining high-paying careers. Specifically, they were comparing the salaries that recent college graduates earn to their Bachelors degrees. This chart shows a summary of the top degrees:

Best Undergrad College Degrees By Salary

Methodology Annual pay for Bachelors graduates without higher degrees. Typical starting graduates have 2 years of experience; mid-career have 15 years. See full methodology for more.

As you can see graduates with physics degrees are the 7th highest-paid in this study (and only behind various physical-science engineering majors). These results are very surprising to me--it's not like they only studied different kinds of science degrees. For example, we can find degrees like art, physical training, and education on the list as well. Does this mean that everyone should go to college to major in petroleum engineering? Of course not! But, ... ... a few questions for you:

1. What other important factors (when choosing a college major) are not considered in this study?
2. Are you surprised by the results?
3. Would you use data from a study like this to help you to make a decision about what you'd like to study in college? If not, what do you considered to be more influential on your decision?
4. Many students say they'd like to become teachers. According to this study, what is the starting median pay for graduates with an education degree?
5. As discussed above, the degree a bachelors degree in physics ranks 7th. What kind of job (or where does a person work) does person with a physics degree have? What would they do? 

Momentum Problem

Photo by takomabibelot.

We've been studying momentum in class this week. As I was putting together some problems for students to use as review, I searched the internet to see if I could find a ready-made collection of problems for high school students that an instructor was willing to share. One of the first hits I found contained this problem:

A bus of mass 19,000 kg driving at 17 m/s runs into a brick wall and comes to a complete stop. What is the force of impact on the bus?*

 I quickly decided that I'd better not use this problem set--something is not right here! Can you see what I mean? Why is this confusing or misleading?

(*) I changed the nouns and numbers in this problem to protect the original author from ridicule. (And also so that a quick Goolge search doesn't immediately turn up this exact question as posed by a frustrated student.)

Planets, Attract!

Images from NASA JPL, assembled by Royalty-free Image Collection.

As we've learned, every object (with mass) in the universe attracts every other object (with mass) in the universe with a gravitational force. Newton's Law of Universal Gravity tells us how to compute the magnitude
of these gravitational forces. Consider the 8 planets in the Solar System:

1. Which of the 7 other planets exerts the largest force on the Earth? How big is this force?
2. Which 2 planets exert the largest forces on each other? How big are these forces?
3. Compare the force of gravity that the sun applies to the Earth and the force of gravity that the Moon applies the the Earth... ... By what factor is the Sun's force stronger?
4. What is the nearest star to the Sun? How far away is it in units of meters?
5. What is the magnitude of the gravitational force between the Sun and its nearest stellar neighbor?

A few years ago, answering these questions would have required a student to look up masses and distances in a handbook (or online) and do many tedious calculations. Now, there are many slick alternatives. I'd like us to investigate these questions using Wolfram Alpha. (Incidentally, Wolfram Alpha is scheduled to have a big overhaul this Wednesday--there will now be a "Pro" version.) Use Wolfram Alpha to determine the answers to the five questions above. Post your results as comments.

Thinking about the Science Fair

Photo by Mars P.

Getting Started

The complete informational packet for the 16th Annual St. Clair County Science and Engineering Fair is now posted online.

1. There are three major project categories. What are they?
2. What are the maximum allowable dimensions for a high school science fair project's display?
3. What would be the proper way to cite a Times Herald newspaper article called "Great Lake are Really Great"? The article was written by Joe Smith on January 17, 2012.
4.  Draw a rectangle on your page. If this rectangle represents a typical 3-sided display board, label the major components.
5. What is the difference between an independent variable and a dependent variable? Give an example of each for a hypothetical experiment.
6. What is an abstract? How long should it be?

Choosing a Project Type

One of the first choices to make when thinking about what you want to do with your project is deciding whether to do an engineering project or a science project. Use the Science Buddies' site to answer the following questions.

1. What are the steps of the typical "engineering design process"?
2. What steps are similar when comparing the "engineering design process" and the "scientific method"?

Choosing a Specific Project

Often, the hardest part about doing a science fair project is selecting a topic to study. It's best to choose a topic that interests you. Coming up with an original idea is nice, but sometimes we need a little inspiration.

1. Do a Google image search for winning science fair projects. Try to draw some quick generalizations... ... Are there any similarities among various winners (not in their subjects, but in their presentation or style)?
2. There are many resources online with science fair project ideas. Let's use the one featured at education.com. Browse through the list, read them, and write down at least three topics that you might find interesting. Make sure your choices are not the same as anyone else sitting near you in class (we want unique projects!).

Note about comments: comments have been disabled for this post because this is a specific outline we're following as an in-class assignment.

Microcontroller Projects

Honors Physics II students recently completed their Arduino-based microcontroller projects. Check out this sweet laser MIDI guitar! Videos of each project can be found on our YouTube channel (accessible from the right sidebar of this page).

Exam Week

Photo by Sashamd

Exams are this week! Students will (hopefully) be studying like crazy in preparation for the big tests. I thought it would be an appropriate time to build a list of some exam taking tips. List any tips or suggestions you've heard about studying or taking exams. These can range from the sound, like being sure to get enough sleep the night before the test--to the ridiculous, like being sure to bring your lucky coin so you can flip it to answer the true/false section of your physics exam.

What advice or tips have you heard? Do you actually plan to use any of them?

Looking Back at First Semester

Photo courtesy of iStock.

This is the last week of first semester. We've encountered many physics topics so far, ranging from the trivial to the complex, and from the mundane to the exciting. Let's spend a few minutes reflecting on what we've done so far:

1. What do you think has been the most difficult topic we've covered so far?
2. What do you think has been the most exciting / thought-provoking topic?
3. Which topic would you have preferred to skip altogether?
4. Which topics have been the most mathematically challenging (this may or may not be the same as the answer to question 1)?
5. Are there any things you'd like to be done differently in second semester?

Do you agree or disagree with what other commentators are saying?

Gravity Sims

Four objects are shown gravitationally interacting.

In physics, we are studying the concepts of universal gravitation--the idea that every object in the universe with mass attracts every other object in the universe with mass. This force is directly proportional to the the product of the two masses involved and inversely proportional to the square of the distance between the objects.

Our friends over at PhET have created a really cool gravity simulator graphing application. It can be found here. Head over to the PhET website and spend some time experimenting with the tool. Be sure to manually adjust the settings as well as to try all of the presets.

1. Which of the presets is the most "complicated" looking?
2. Which of the presets is your favorite? Why?
3. Under what conditions does the motion closely resemble circular motion?

Angry Projectiles

Angry Birds, available for a multitude of devices from Rovio.

It seems as though the talk of the school's hallways this holiday season is Angry Birds. I've heard countless students discussing playing the game on their new devices. To be honest, the popularity of the game is a bit of a mystery to me... ... I just don't find it all that much fun. I think puzzle games like Cut the Rope or Where's My Water are more challenging and fun, and they make better use of a muti-touch environment. For simple arcade fun, it's tough to beat Fruit Ninja. Perhaps the popularity of Angry Birds is not because of its awesome gameplay, but rather because of its ubiquity--one can play Angry birds on every make and model of computer or smart phone.

In any case, we are currently studying projectile motion in our physics class. If you think about it, the birds (and their "weapons") from Angry Birds can be thought of as projectiles. They fly through the air along parabolic trajectories. That got me thinking... ... what other "classic" games are variations of a similar idea? It seems like many games' primary control feature is that the player adjusts the elevation of some type of projectile launcher.

A few questions for consideration... ...

1. Do you like Angry Birds? Is it a great game?
2. Should we consider the angry birds to be projectiles (from a strict physics sense)? Explain.
3. What other games have you played where you are mainly adjusting the angle of inclination (elevation) of a projectile launcher? Are these fun games?

Sunrise, Sunset

Photo by Politikaner.

The winter solstice has come and gone (on December 22, 2011) for us. The solstice marks the shortest day of the year. It might come as surprise, then, to learn that December 22 was neither the day of the latest sunrise nor the earliest sunset. This seems counter-intuitive, doesn't it? To see what's going on here, let's try to answer a few questions. So that more can participate, please limit your response (at least initially) to just one question.

1. What was the date of the earliest sunset for Port Huron (in December, 2011 or January, 2012)? At what time did the sun set on this date?
2. What was the date of the latest sunrise for Port Huron (in December, 2011 or January, 2012)? At what time did the sun rise on this date?

Do a search for the word "analemma" and read about it.

1. What causes the analemma?
2. How is the analemma related to the earliest sunset and latest sunrise?