# Everyday Physics: Dancing

by Sarah McPherson, AP Physics 1

When looking at a dancer, the eye sees impressive movement. Behind every performance are hours of practice, sweat, and dedication. After it’s all broken down, one can find the clockwork in dancing – physics.

A major factor in dancing is balance. Dancers have to focus on their centers of gravity when performing, for if they lean too far forward, their center of mass could go beyond the base of support, and they could fall. Balancing is even more difficult if there are partners dancing together; however, dancers can use physics to their advantage. If their centers of gravity are used correctly, the end result can be a stunning visual. For their centers of gravity to be supported, physical connection, or tension, is needed. The partners pulling on each other can help each other balance. The diagram below is a great illustration of the forces working on them.

The force of gravity is pulling them down and keeping them on the floor; likewise, the weight vectors from their centers of gravity point directly down, even though they are slightly tilted. Without the tension of their arms holding each other, both of the dancers would more than likely fall – especially the girl. Holding themselves together in this fashion creates one unit with a center of mass located somewhere between each dancer and over the base of support offered by the male dancer’s feet.

Physics also applies to swing dancing. This partner dance requires focus and momentum. For example, a very famous move in swing dancing is called “The 6 O’clock.” The female partner is directly above the male partner with her arms wrapped around his neck. The female is representative of the hour hand while her counterpart is the minute hand.

In order to reach this position, the female has to get a running start to reach the male, and then jump high enough for him to catch her. The woman’s kinetic energy during running is converted to gravitational potential energy with the assistance of the man performing work to lift the woman higher.

Though it may seem unlikely, physics is a key part of dancing. Without this science, the dancers wouldn’t be able achieve certain movements and the dance would be dull. Physics brings excitement to the dance!

Reference: http://www.hep.uiuc.edu/home/g-gollin/dance/dance_physics.html.

About the author: Sarah McPherson is a student in AP Physics 1 and is also the Drum Major for the Marching Grizzlies. In addition, she is the artist of the featured image in the page header.

# Roller Coaster Physics

Carden with his model “G Money.”

### The creation of a model:

Kendra and Leslie with their model of “No Clue.”

By kimgeddes

# Earth, Physics and Imagination

by Leslie Medina, AP Physics 1 student

Painting by Leslie Medina

When I think of Mother Earth, I imagine hearing a pulse, and I visualize all the natural beauty that Earth contains. When I give such human-like qualities to Earth, I envision her breathing, even though I know this is not how things work. I think about all the possibilities and opportunities that Earth has given us. The ability to live, explore, and gain knowledge about our universe and the galaxies that endlessly fascinate us. When I depicted Earth breathing and exhaling, I was visualizing how Earth metaphorically takes in knowledge of its surroundings.

With this knowledge, there is an even greater desire to learn more about Earth, space, and life itself. Physics explores many things concerning these expansive topics and attempts to offer an explanation of all the extraordinary phenomena that surround us. On my painting, various equations and key details concerning gravity, orbits, and planets, appear as stars in the night sky. What I’ve come to realize is that these equations not only fill up the background space of my painting, but they also fill up the spaces in our curious minds with an abundance of knowledge.

Leslie Medina is an Honors/AP student at Creekview High School, and she is also an amazing artist.

Image

# What are Dark Matter and Black Holes?

by Briana Purves, 6th period CP Physics

Most people consider dark matter and black holes to be mysteries; however, with the help of scientists and technology, these mysteries can be understood! Dark matter is a nonluminous material that exists in space and can appear in many different forms. Black holes are a region of space with a gravitational field so intense that no matter or radiation can escape it. Black holes also have the ability to deflect light, but dark matter does not. Overall, there are many things that we can learn about both dark matter and black holes.

Nonluminous, dark matter is postulated to exist in space and can take any of several forms, including weakly interacting particles or even high energy randomly moving particles created soon after the Big Bang. Although it is not in the form of visible stars and planets, scientists have deduced the existence of dark matter because there is not enough visible matter in the universe to account for the gravitational effects present in the universe. Research supports that dark matter makes up a substantial percentage of the matter-energy composition of the universe, while the rest is dark energy and “ordinary” visible matter. Dark matter is not in the form of dark clouds filled with normal matter, but can be seen as matter made by baryons particles that are composed of protons, neutrons, and electrons.

Dark matter was originally known as the “missing mass” until Fritz Zwicky discovered that the mass of all the stars in the Coma Cluster of galaxies provided about one percent of the mass required to keep the galaxies from escaping the cluster’s gravitational pull. Missing mass remained a question until the 1970s when two American astronomers proved its existence through the idea that the mass of the galaxy within the orbit of stars must increase linearly with the distance of stars from the galaxy’s center. Also, dark matter is not capable of being composed of antimatter, because scientists would be able to see gamma rays that have been produced when antimatter annihilates with matter. Scientists are still unsure of the exact composition of dark matter, but the most common view is that dark matter is made up of exotic particles called axions, or weakly interacting massive particles.

Conversely, black holes are a region of space that has a gravitational field so intense that no matter or radiation can escape it. The gravity of a black hole is so strong because the matter has been squeezed into the tiny space, not allowing it to escape. People cannot see black holes, as they are invisible to the human eye, and can only be detected by advanced special telescopes. Black holes come in many different sizes and shapes, from the size of a large planet to as small as just one atom. Even the extremely small black holes contain massive amounts of matter inside.

One type of black hole that has been discovered is called a Stellar. Stellars can grow to be up to twenty times as big as the mass of the sun; however, there are black holes that can grow to be even bigger; these black holes are called Supermassives. Supermasssives can have masses up to one million times greater than the sun’s mass. Scientists have found that these Supermassive black holes are most commonly found in the Milky Way (also known as Sagittarius A) and have a mass equal to four-million suns and a few million earths.

Black holes are formed when the center of a star falls in on itself causing a supernova or when an exploding star blasts parts into space. Many black holes cannot be seen today because of the strong gravitational pull of light into the center of the hole. When a black hole and a star are near each other, high energy light is made that can only be seen by satellites and telescopes in space.

Einstein’s Law of General Relativity explains why black holes deflect light. Einstein’s law states that a ray of light arriving from one side of an object is bent inwards so that its apparent direction of origin, when viewed from the opposite side, is seen as a different angle. The observed gravitational effect between masses will result from their warping of space-time. Einstein’s Law of General Relativity predicts that every object’s gravitational field bends light rays which is called gravitational lensing. According to Wikipedia, “A gravitational lens is a distribution of matter between a distant source and an observer, that is capable of bending the light from the source, as it travels towards the observer.” Einstein’s Law of General Relativity also supports that the gravitational fields of massive objects causes a distortion in space-time. Einstein’s Law of General Relativity proves just how black holes have the capability to deflect light, as they are able to bend light rays through its gravity.

People have the capability of learning infinite things about both dark matter and black holes. Such things can include how dark matter is known as a nonluminous material that is postulated to exist in space and that can take any of several forms, while, contrarily, black holes are known as a region of space that has a gravitational field so intense that no matter or radiation can escape. Black holes also have the capability to deflect light, which can be proven by Einstein’s Law of General Relativity and through gravitational lensing. If all of these things can be learned about dark matter and black holes through the writing of this one essay, imagine what can be learned throughout a lifetime.

Briana Purves is not only an excellent physics student, she is an outstanding softball player.

# Particles and waves: The central mystery of quantum mechanics – Chad Orzel

Thank you to Ted-Ed for this lesson on the dual nature of light.

“One of the most amazing facts in physics is that everything in the universe, from light to electrons to atoms, behaves like both a particle and a wave at the same time. But how did physicists arrive at this mind-boggling conclusion? Chad Orzel recounts the string of scientists who built on each other’s discoveries to arrive at this ‘central mystery’ of quantum mechanics.”

# The Physics behind “Angry Birds”

Photo credit: https://d1guvqt7k9h5xe.cloudfront.net/AcuCustom/ Sitename/DAM/005/red_400x400.jpg

by Emily Lehman and Meghan Nay

We are avid Angry Birds fans, so when our physics teacher offered us the opportunity to analyze the validity of physics principles underlying the game, we accepted eagerly. We conducted an analysis to determine whether the mobile application “Angry Birds” followed the principles of physics – specifically, principles of projectile motion.

We videoed the game from the initial launch of a bird to his collision with the pig pedestal. Then, we used Tracker software to collect data of the bird’s motion. Here’s our procedure:

1) We uploaded the video of the red angry bird into the software,Tracker.

2) Using Tracker, we found the horizontal and vertical position vs. time graphs. From there, we found the equation of the best fit line/curve.

3) After obtaining the equation of best fit for the position vs. time data, we took the derivative in order to find the velocity vs. time equation.

4) Then to find the acceleration vs. time equation, we took the derivative of the velocity vs. time equation.

5) Using the position, velocity, and acceleration equations, we were then able to analyze the bird’s motion and compare it to the laws of projectile motion on Earth.

6) Since we don’t know any of the measurements in the video, we established an arbitrary unit of length using the pig pedestal in the video. All equations are based on a unit of length we have called a “pig pedestal.”

Data and Analysis:

Position vs. time data using Tracker. The straight line is the horizontal position vs. time, and the concave-down parabola is the vertical position vs. time.

The graph above shows the position of the bird in the x and y directions. The best fit line for the graph in the y direction is the equation y = -1.882t² + 6.833t + 1.993. To find the velocity of this position graph we took the derivative and found the equation of the velocity in the y direction to be v = -3.764t + 6.833. Also, to find the acceleration in the y direction we found the derivative of the velocity equation and found the acceleration in the y direction to be a=-3.764 pig pedestals/s².

We repeated these steps to find the equations of the position, velocity, and acceleration graphs in the x direction. Which in subsequent order the equations of these graphs are x = 4.637t – 0.0668, v =4.637 pig pedestals/s, and a = 0 pig pedestals/s².

X-Direction

Position vs Time: s(t) = 4.637t – 0.0668

Velocity vs Time: s'(t) = v(t)= 4.637 pedestals/s

Acceleration vs Time: s”(t) = v’(t) = a(t) = 0 pedestals/s²

Y-Direction

Position vs Time: s(t) =-1.882t² + 6.833t +1.993

Velocity vs Time: s'(t) =v(t) =-3.764t + 6.833

Acceleration vs Time: s”(t) = v'(t) = a(t) =-3.764 pedestals/s²

We assumed that the Angry Birds game takes place on Earth where the acceleration due to gravity is -9.8 m/s². Using the vertical acceleration from the best fit line, we  set -3.764 pig pedestals/s2 equal to -9.8 meters/s2  which determined the height of the pig pedestal to be 2.603 meters.

Conclusion:

Based on our findings, we were able to determine that “Angry Birds” follows the rules of physics for a number of reasons. The acceleration of the bird in the x direction was zero, which is characteristic of an object launched as a projectile on Earth, assuming no air resistance. Also because the position vs. time graph in the y direction closely followed the kinematics position equation, we determined that the Angry Bird is subject to a gravitational force.

We also made some strange or odd discoveries about the game. Using the unit conversion discussed in the Analysis section, we found that the actual size of an Angry Bird is 1.019 meters tall, which is around 3.3 feet. We derived this number from the position vs. time graph in the y direction. We found the acceleration to be -3.764, but this was not meters/second2; the units for this was pig pedestals/second2. By assuming gravity in “Angry Birds” was -9.8, we used conversions to find the height of the pig pedestal. Then, we were able to find the height of the bird, which was 1.1019 meters. Certainly, a bird of this size would be subject to air resistance; however, the data show no force in the horizontal direction!

Photo credit: http://resources0.news.com.au/images/ 2012/09/16/1226475/242180-rheinmetall-039-s-simulators-in-use.jpg

Determining that one video game followed the rules of physics on Earth opens up many possibilities for real world applications. Virtual simulations have the potential to revolutionize society and many fields of work. For example, virtual simulations are extremely helpful in pilot training or training for warfare. The analysis that we undertook could be used to assess the validity of these simulations and thus gauge their acceptability as effective training tools.

By kimgeddes

# Incorporating Computer Models into Traditional Physics Labs

Photo: Students collecting motion data.

In an effort to achieve consistency with current expectations of university physics students in rigorous science and engineering programs, I have implemented laboratory investigations that seek to provide students with opportunities to explore real world motion using modern tools and techniques that are grounded in fundamental physics principles. My goal is for the students to be able to:

• Observe and video everyday motion and then analyze the video to extract motion data.
• Apply fundamental physics principles to analyze and describe the motion and then to develop computer models that explain and predict motion based on these principles.
• Effectively communicate results (the observations, the models, and comparisons between them).
• Critique their own work and the work of their peers.

My students have completed their first assignment that required that they explore the effects of air resistance by observing the motion of an object dropped from rest and allowed to fall straight down. The students were instructed to choose an object that would be noticeably affected by air resistance. The students selected objects such as coffee filters, Styrofoam lunch trays, crumpled paper, etc., and the adventure began. The students posted their final results on YouTube to allow for peer assessment of their final products.

I was very pleased and impressed with my students’ motivation and ability to meet this challenge. At first, some of them were intimated by working with computer code but quickly became comfortable with this new method of analyzing motion. Some sample student projects are provided below:

# This Is The Physics Lesson Of The Future, And It Looks Insanely Fun (FastCoDesign)

Photograph by Celine Grouard for Fast Company.

An afternoon at the playground might be the perfect time to introduce kids to physics. SciPlay, part of the New York Hall of Science, is working to develop an app to teach middle school students the Newtonian mechanics of the playground. FastCoDesign reports:

The SciPlay app is essentially an annotated video: Using an iPad, you film motion–running, jumping, swinging, sliding, throwing a ball, etc.–and the app visualizes the basic science at work, pinpointing moments and levels of velocity, acceleration, energy, and force. Through manually tracing the arc of motion of the ball or person, or by using sensor data from the iPod attached to a ball or a kid’s belt, it superimposes the force diagrams that make up the backbone of any classroom physics lesson on real-life situations.

According to the article, the developers plan to…

View original post 12 more words