http://www.sciencebuddies.org/mentoring/project_ideas/home_Phys.shtml?gclid=CPHXt9L9v44CFRZLYQodgH1hgQ

Objective

The goal of this project is to build a roller coaster for marbles using foam pipe insulation and to investigate how much of the gravitational potential energy of a marble at the starting point is converted to the kinetic energy of the marble at various points along the track.

Introduction

Slow and clanking, the string of cars is pulled up to the crest of the tallest point on the roller coaster. One by one, the cars start downhill on the other side, until gravity takes over and the full weight of the train is careening down into curves, twists, and turns. The roller coaster is a great example of conversions between potential energy (stored energy) and kinetic energy (the energy of motion). As the cars are being pulled up to the top of the first hill, they are acquiring potential energy. The chain that pulls them up the hill works against the force of gravity. At the top of the hill, the cars' potential energy is at it's maximum. When the cars start down the other side, this potential energy is converted to kinetic energy. The cars pick up speed as they go downhill. As the cars go through the next uphill section, they slow down. Some of the kinetic energy is now being converted to potential energy, which will be be released when the cars go down the other side.

Potential energy comes in many forms. For example, chemical energy can be stored and later converted into heat or electricity. In the case of a roller coaster, the stored energy is called "gravitational potential energy," since it is the force of gravity that will convert the potential energy into other forms. The amount of gravitational energy can be calculated from the mass of the object (m, in kg), the height of the object (h, in m), and the gravitational constant (g = 9.8 m/s2). The equation is simply: gravitational potential energy = mgh.

Kinetic energy is the energy of motion. The amount of kinetic energy an object has is determined by both the mass of the object and the velocity at which it is moving. The equation for calculating kinetic energy is: kinetic energy = 1/2 mv2, where m is the mass of the object (in kg) and v is the velocity of the object (in m/s).

You've probably noticed that the first hill on the roller coaster is always the highest (unless the coaster is given another "boost" of energy along the way). This is because not all of the potential energy is converted to kinetic energy. Some of the potential energy is "lost" in other energy conversion processes. For example, the friction of the wheels and other moving parts converts some of the energy to heat. The cars also make noise as they move on the tracks, so some of the energy is dissipated as sound. The cars also cause the supporting structure to flex, bend, and vibrate. This is motion, so it is kinetic energy, but of the track, not the cars. Because some of the potential energy is dissipated to friction, sound, and vibration of the track, the cars cannot possibly have enough kinetic energy to climb back up a hill that is equal in height to the first one. The way that physicists describe this situation is to say that energy is conserved in a closed system like a roller coaster. That is, energy is neither created nor destroyed; there is a balance between energy inputs to the system (raising the train to the top of the initial hill) and energy outputs from the system (the motion of the train, its sound, frictional heating of moving parts, flexing and bending of the track structure, and so on).

You can investigate the conversion of potential energy to kinetic energy with this project. You'll use foam pipe insulation (available at your local hardware store) to make a roller coaster track. For the roller coaster itself, you'll use marbles. By interrupting the track and allowing the marble to continue on a smooth, level surface, you'll measure the velocity of the marble at different points along the track. >From the velocity and the mass of the marble, you'll be able to calculate the marble's kinetic energy at the different track locations.

For each track configuration, you should try at least 10 separate tests with the marble to measure the kinetic energy. How much of the marble's gravitational potential energy will be converted to kinetic energy? A foam roller coaster for marbles is easy to build, so try it for yourself and find out!

Terms, Concepts and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

Potential energy (stored energy) Kinetic energy (energy of motion) Conservation of energy (basic law of physics) Gravity Velocity Friction Slope (rise/run)

Questions

What is the equation for calculating an object's gravitational potential energy? What is the equation for calculating an object's kinetic energy? The marble has its maximum gravitational potential energy when it is at the starting point: the

highest point on the roller coaster. How much of this potential energy is converted to the marble's kinetic energy?

Bibliography

Here's a good webpage on kinetic and potential energy applied to roller coasters:Merritt, T., M. Lee and B. Colloran, 1996. "The Physics of Amusement Parks: Kinetic and Potential Energy," ThinkQuest Library [accessed August 23, 2007] http://library.thinkquest.org/2745/data/ke.htm.

This short animation explains kinetic energy and potential energy:Brain POP, date unknown. "Kinetic Energy," Brain POP® Animated Educational Site for Kids [accessed August 23, 2007] http://www.brainpop.com/science/energy/kineticenergy/.

Here are some more quantitative explanations of kinetic and potential energy: o Henderson, T., 2004. "Work, Energy, and Power," The Physics Classroom and Mathsoft

Engineering & Education, Inc. [accessed August 23, 2007] http://www.physicsclassroom.com/Class/energy/u5l1c.html.

o Nave, C.R., 2001a. "Kinetic Energy," HyperPhysics, Department of Physics and Astronomy, Georgia State University [accessed August 23, 2007] http://hyperphysics.phy-astr.gsu.edu/hbase/ke.html.

o Nave, C.R., 2001b. "Potential Energy," HyperPhysics, Department of Physics and Astronomy, Georgia State University [accessed August 23, 2007] http://hyperphysics.phy-astr.gsu.edu/hbase/pegrav.html#pe.

Materials and Equipment

To do this experiment you will need the following materials and equipment:

At least two 6 foot (183 cm) sections of 1-1/2 in (about 4 cm) diameter foam pipe insulation Glass marbles Utility knife Masking tape Tape measure Bookshelf, table, or other support for roller coaster starting point Stopwatch

Gram scale for weighing marble Length of Masonite (smooth hardboard) for marble to travel on (for measuring velocity at

different points along the track). You can glue the Masonite into a V-shape, and paint it with alternating stripes at 5 or 10 cm intervals. The V-shape keeps the marble going straight, and the stripes allow you to easily measure the distance the marble has traveled during a timed interval.

Optional: video camera and tripod

Experimental Procedure

Note: use the utility knife with care. A fresh, sharp blade will make cutting the insulation easier. 1. Do your background research so that you are knowledgeable about the terms, concepts, and

questions, above. 2. Cut the foam pipe insulation in half (the long way) to make two U-shaped channels.

a. The illustration below shows the foam pipe insulation, end-on.

The illustration above shows the cross-section at one end of the foam pipe insulation.b. The insulation comes with one partial cut along the entire length. Complete this cut

with the utility knife (yellow circle in the illustration above). c. Make a second cut on the other side of the tube (yellow line in the illustration above),

along the entire length of the tube. d. You'll end up with two separate U-channel foam pieces. You can use masking tape to

attach pieces end-to-end to make the roller coaster track as long as you want. 3. To make a roller coaster track, tape two (or more) lengths of the foam U-channel together,

end-to-end. The joint between the two pieces should be as smooth as possible. 4. You can make the track as simple or as complex as you'd like. You can add curves, loops, and

additional uphill and downhill sections. The illustration below shows two examples. You'll find that one requirement is that the starting point be the highest point on the track.

The illustration above shows two different roller coaster tracks for marbles. How much height is needed at the starting point in order for the marble to loop the loop?5. In order to measure the velocity of the marble, you'll need a way to measure how much

distance the marble travels during a measured time interval. a. A good way to do this is to interrupt the foam track and direct the marble along a

smooth, level surface (e.g., two long pieces of Masonite glued in a V-shape). Support the Masonite V (with cardboard, beanbags, etc.) so that it is level with the end of the foam track.

b. Paint the Masonite with 5 or 10 cm long stripes in contrasting colors (e.g., red and white or black and white) so that you can use it to measure distances.

c. Use the stopwatch to measure the time it takes for the marble to travel a certain length along the Masonite track.

d. You can also videotape the marble, and use the measuring stick to measure the distance the marble travels in successive frames (each standard video frame is 1/30 second).

6. Measure the height of the starting point for the track. 7. Measure the mass of the marble. 8. Calculate the gravitational potential energy of the marble at the starting point. 9. Run a single marble down the track 10 separate times.

a. For each run, use your striped measuring stick and stopwatch to measure the velocity of the marble as it completes the track.

b. Calculate the average of your 10 measurements. c. More advanced students should also calculate the standard deviation.

10. From your velocity measurement and the mass of the marble, calculate the kinetic energy of the marble.

11. Repeat the velocity measurement at various points on the track by cutting the track and allowing the marble to continue on in a straight line on a smooth surface. Use your striped measuring stick and stopwatch to measure the velocity of the marble.

12. Does the marble's kinetic energy ever equal or exceed its initial gravitational potential energy?

Variations

Here are just a few of many possible variations on this project. Perhaps these will stimulate your thoughts about other experiments you could try:

How much kinetic energy is required for various track features? For example, how much kinetic energy is required for a marble to successfully navigate a loop in the track?

You can expand the experiment by building a set of roller coaster tracks with various loop sizes. How does the kinetic energy requirement change when the loop diameter increases? How does the kinetic energy requirement change when the loop diameter decreases?

If you can find spheres that have equal diameter but made from different materials, you could investigate how the mass of the sphere affects how well it travels along the track.

Maybe you noticed that your loop wobbles a bit as your marble passes through it. The energy to move the track comes from the marble. The energy that the marble loses to make the track move means less energy is available to make the marble itself move. Can you think of a way to stabilize the loop so that it doesn't wobble? Does the marble have more kinetic energy after exiting the stabilized loop? Design an experiment to find out!

Try using different lengths of roller coaster track so that you can adjust the initial slope of the track. Keep the starting height the same, but change the slope by adding additional track length. (Remember, slope is rise/run, so you'll be holding the "rise" constant, and gradually increasing the "run.") How do you think the kinetic energy of the marble will change as you change the slope of the track?

For a more basic version of this experiment, see the Science Buddies project Roller Coaster Marbles: How Much Height to Loop the Loop?.

Credits

Andrew Olson, Ph.D., Science Buddies

Objective

The goal of this project is to design and do experiments that demonstrate which skateboard wheels are best for speed and maneuverability.

Introduction

The fast moving, slip-sliding sport of skateboarding looks like pure fun, but it's also an activity chock full of science. Those rotating wheels speeding along smooth cement parks or clicking across bumpy sidewalks follow the same laws of friction and rotational momentum as the classic incline plane and trolley in a physics lab. The glide you enjoy after initial push off on your board demonstrates, at least briefly, the constant speed or velocity from inertia, and the slow roll to a stop indicates that frictional forces have finally robbed you of your forward motion. Skateboarding, that high flying sport of athletic anarchists, blends balance, speed, and spunk with real life, in-your-face demonstrations of force, motion, and frictional drag.

This project focuses on testing skateboard wheels. The video highlights two skateboarders, Chuck and Jake, who decided to take the scientific approach to investigate the importance of wheel size to their ride. They knew that large wheels are supposed to be faster than smaller wheels, according to seasoned skateboarders and skateboard manufacturers. So they put the theory to the test. They set up two experiments to compare large wheels (60 mm diameter) to small wheels (50 mm diameter) in speed and maneuverability. Check out the video to see their results. Then read on to see how you can test their theory in a set of experiments of your own.

Jake and Chuck's approach and experimental design were definitely on target. They changed only one variable (wheel diameter) to run their experiments while keeping other variables like track distance,

Click here to watch a video of this investigation, produced by DragonflyTV

and presented by pbskidsgo.org

board size, rider weight, and skill level constant. They carefully clocked their times to tenths of a second. Still, the results surprisingly showed no difference between the large and small wheels in speed down the flat and only a slight difference in ability to successfully turn through a short obstacle course. Wheel size alone wasn't enough to make a measureable difference, at least in their experiments. If you were to repeat theses experiments would you get different results using your board, local terrain, and different sets of wheels?

The challenge of this project is to design experiments that can verify the advertised speed and performance differences between skateboard wheels. The results don't have to be huge; tenths of a second may be enough. But the differences have to be consistent and large enough to be detectable in your experiments. It's all about wheel choice and surface selection in this project.

For starters, why not set up longer test runs than they showed in the video so that there's more distance to travel and time to pick up possible differences in speed or performance of the wheels. When selecting the wheels for your tests, consider not just size but other factors that determine speed, grip and maneuverability. For example, the "hardness" of a wheel, its width, and the shape of the wheel's edge (rounded, beveled, or straight) all contribute to how fast a skateboarder can cruise, fly vertically, or turn sharply. The type of surface you skate on is another variable since soft wheels give a smooth but slower ride over bumpy terrain while hard wheels take on slick runs with greater speed but a rougher ride. Your task is to study these variables and come up with the best wheel choices to get the most "extreme" results with your board in your chosen terrain.

Modern day skateboards have come a long way from the homemade clunky contraptions of metal skate wheels nailed to the bottom of a short 2 x 4 board. The wheels, in particular, illustrate the synergy of space-age products with the development of an entire sport centered around flips, turns, verticals and the desire for speed and a sense of flight. Skateboard wheels have morphed into synthetic, highly engineered structures made from resilient, lightweight and durable plastics that encase sleek metal ball bearings to provide the smoothest and fastest spin. These designs have come about to large degree from manufacturing engineers applying a solid understanding of the physics of wheels and rotational motion.

Plastic materials, like the polyurethanes used in skateboard wheels today, are slicker than metal so they decrease the frictional forces between the wheel and the surface. This translates into both a smoother ride and increased speed per push. The relative hardness or softness of the plastic wheels also creates subtle but important differences in how the wheels roll. Generally, hard wheels mean greater speed, while softer wheels travel more slowly because they interact more with the tiny bumps in the road as you move along. As the young boarders in the video suggested, the diameter of a skateboard wheel affects speed as well. A larger wheel rotates over a longer surface distance per revolution than a smaller wheel, so larger wheels produce more speed per push, if all other factors are equal.

Which combination of wheel characteristics do you think will show the most dramatic differences in speed and maneuverability on your board? Should you use large, soft wheels with a square edge and run those against small, hard wheels with a round edge? Or should you use some other combinations of wheels? How will the wheels you select for the flat course hold up in a slalom test of turning ability? Will the slower wheels in the straight away actually turn out to be better in the rapid turns of the timed slalom course or the hard, slow turns of a maneuverability test? Can you explain your wheel choices and their eventual results based on the science of the friction and rotational motion?

To find out, start by doing some background research on skateboard wheels and the basic physics that describes their spin and speed. We've listed some suggested search terms and basic questions in the next section. Organize what you learn or know about skateboard wheel performance according to diameter, hardness, width, and shape using the summary table below. That should help keep the basic details straight and make your choices of which wheels to test in your experiments a little easier. Then bolt those wheels to your trucks, hop on your board, and run your experiments to find out if your scientific instincts are as awesome as your skateboarding skills!

Skateboard Wheels Performance Summary

Wheels Effect on Speed

Effect on Grip

Effect on Turns

I. Diameter (mm)  

Large Wheels (60+)   N/A N/A

Medium Wheels (56-60)   N/A N/A

Small Wheels (52-55)   N/A N/A

II. Hardness (A)  

Hard (97-105)     N/A

Medium (94-96)     N/A

Soft (85-93)     N/A

III. Width  

Wide      

Narrow      

IV. Edges  

Square      

Beveled      

Round      

Terms, Concepts and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

Skateboard wheels Friction (rolling friction and static friction) Velocity Acceleration Momentum Rotational motion Newton's First Law of Motion (inertia) Newton's Second Law of Motion (Force = mass × acceleration)

Questions

How is friction important in the push off and in the rolling speed of a skateboard wheel? How do large wheels differ from small wheels in surface frictional forces?

Explain how Newton's first law of motion applies to skateboarding. Describe how large, hard wheels perform differently than small, soft wheels. Describe the

advantages of using large, soft wheels versus small, hard wheels. Describe how the width of a skateboard wheel affects the grip and slide of a skateboard. Describe how the edge shape of a skateboard wheel can affect the ride of a board and what a

skater can do on the board. What is polyurethane? Why is it an excellent material for skateboard wheels?

The goal of this project is to explore how changing your center of gravity affects how well you can balance.

Introduction

The project video below focuses on three talented students at a circus arts school. The girls performed one of the most difficult circus acts, walking the tightrope. They knew from experience that it was easier to balance on the tightrope when they held a balancing pole in front of them instead of just using their arms stretched out to the sides. But they wondered if the length of the pole would make any difference in their ability to successfully walk the wobbly rope.

The girls decided to develop an experiment to answer their question. Each of them attempted to walk across a low tightrope using poles of three different lengths, and they counted the number of times they wobbled or fell with each pole. They found their balance improved as the pole length got longer. They figured that holding a long balancing pole was like having "super-long arms" to help keep them upright on the rope.

In this project, you can do a similar experiment without having to worry about falling from a circus tightrope. In fact, your balancing challenge need only go as high as a roadside curb in these experiments. You'll stand on a curb with your heels hanging off of the edge, and ask an assistant to record the number of seconds you maintain your balance. If you find that's too easy a test, you can try to balance while slowly raising your heels up and down or stand on one foot to increase the difficulty.

This curbside balancing act will serve as a simple but useful test to see how changing arm position or holding a pole affects how long you can stay on the curb. Using a short pole or a long pole will help you measure the effect of pole size on your balance. You may not have the fancy costumes or the equipment of a circus performer, but in this project you'll be able to collect interesting data about balance just the same. Read on to see how to organize your experiments and get started on this fun, light-footed project.

As a first step, do some background research on the science that explains the physics of balance. We've provided a list of useful search terms and basic questions in the next section to get you started. One of the major concepts you will need to understand is the idea of center of gravity or center of mass. This is an imaginary point about which all weight (mass) is evenly distributed in an object or in our bodies. It's a little easier to think of the center of mass of a perfectly round object like a ball, because its center of mass is located at the centermost point of the ball. Our bodies are not evenly symmetrical in all directions, but for most people when they are standing, the body's center of gravity is midway between the stomach and back, about two inches below the belly button.

Athletes use the idea of center of gravity to improve their performance in all kinds of sports, dance, and martial arts. Generally, a lower center of gravity in the body means an increase in stability. That's why football players bend down, take a wide stance and shift their weight forward when they block and tackle. This position lowers the center of gravity in their bodies, makes their base of support broader,

Click here to watch a video of this investigation, produced by DragonflyTV

and presented by pbskidsgo.org

and makes it harder to push them over. The same idea applies to cars and buildings where engineers tailor designs to keep the center of gravity low to make safer, more stable vehicles and structures.

Whenever our center of gravity lies directly over the base of support (for example, our feet when standing), we remain perfectly balanced and steady. But every time we move, our center of gravity shifts in response to the change in our shape and the new distribution of mass. This means while standing almost any change in position comes with a risk of falling if our center of gravity shifts too far beyond the base support of our feet. In order to remain upright while doing something as simple as walking, our body must continuously compensate to the changing center of gravity by slightly adjusting our arms, head, and shoulders forward or backward to keep the center of gravity always directly above our moving feet. So there's some complicated mechanics going on even when one takes an easy stroll down the street. Imagine the rapid adjustments the body must automatically make when you try something as challenging as traversing a high wire.

For a high wire performer, the body's natural center of gravity must be kept directly over the wire in order to stay balanced. That's difficult because the base of support (usually just one foot on a thin wire) is so narrow and the wire is constantly moving. Such a limited base of support means just a little too much lean to one side or the other can cause a serious wobble and dramatically increase the risk of falling off the wire, hopefully into a safety net. Anything performers can do to lower their centers of gravity will make their walk on the wire easier. That's where the balancing poles come in. In your curbside experiments, see if you can figure out just how the position, weight, and length of a pole changes your center of gravity and increases or decreases your stability when trying to balance.

You also should notice how using the poles influences the speed of your wobbles on the curb. Physicists explain that bodies rotating around a fixed point, like a tightrope walker falling off (around) a fixed high wire, follow similar laws of torque and angular velocity. Angular velocity is basically how fast an object spins around a pivotal point. Torque is the amount of force that causes an object to rotate about that point. In a general sense, the speed of a spinning object varies in direct proportion to the torque applied to it and in inverse proportion to its length or distance from the pivot point. The more torque, the greater the spin. The longer the distance, the more time it takes the object to complete the entire circle around the pivot point, and the slower the spin.

For a tightrope walker, a foot on the rope represents the pivotal point. When she is not carrying a balancing pole, her head or the fingertips of her outstretched arms mark the maximum distance from the pivot point. Adding long poles to a tightrope walker essentially extends the distance from the pivot point out to the limits of the ends of the poles. So the circus school students in the video were not far off when they said they thought their balancing poles acted like "super-long arms." Check out how well the poles you carry in your experiments serve as long arm extensions and if they slow the speed of your wobble when you try to balance on the curb.

You'll find a few recommended activities on finding your center of gravity in the Bibliography section. Do at least two of the activities before you start your experiments. They will quickly demonstrate how your center of gravity changes as you move or an object's center of mass shifts when you change its shape or weight.

Good luck, have fun, and watch that wobble!

Terms, Concepts and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

Mass Gravity Center of gravity (or center of mass) Rotational motion Torque Angular velocity

Physics of tightrope balancing

Questions

What is the difference between mass and weight? What is the center of gravity (center of mass) of a spherical object? of an irregularly shaped

object? How does center of gravity relate to balance? Where is the approximate center of gravity of a human when standing? when sitting? How do the long poles used by a tightrope walker make balancing easier? What is torque? How does torque influence a tightrope walker? How does a tightrope walker's center of gravity change with the position or an increase in

length of a balancing pole?

Bibliography

As part of your research and preparation, do at least two of the following activities to become better acquainted with the concept of center of gravity:

Quick demonstration of center of gravity using a meter stick and clay :Exploratorium, 1997. "Center of Gravity," Science Snacks, Exploratorium [accessed July 1, 2007] http://www.exploratorium.edu/snacks/center_of_gravity.html.

A simple way to find the center of mass of some interesting shapes:Olesik, S., 2002. "Center of Mass," WOW Project, Ohio State University [accessed July 1, 2007] http://wow.osu.edu/experiments/ntb/centerofmass.html.

Magically balance a cork on the edge of a cup; find the center of gravity of an irregular shape:Schneider, J., 2007. "Center of Gravity," HotChaulk, Inc. [accessed June 30, 2007] http://www.lessonplanspage.com/ScienceExWhereIsCenterOfGravityLocatedMO68.htm.

Finding the center of gravity as you move with a partner:WAW, 2005. "Finding the Balance--Movement and Music Activity", World Arts West [accessed July 1, 2007] http://www.worldartswest.org/plm/guide/activitypages/movemusic/findbalance.shtml.

Easy demonstrations and activities to show how to change center of mass in our body or of paper models :Dorean, E., date unknown. "Balancing Bernie: Sports and Balance," Knight Foundation Summer Institute, Haverford College [accessed July 1, 2007] http://www.haverford.edu/educ/knight-booklet/balancebernie.htm.

The idea for this project came from this DragonFlyTV podcast: TPT, 2006. "Circus by Alex, Sarah and Sasha," DragonflyTV, Twin Cities Public Television [accessed June 30, 2007] http://pbskids.org/dragonflytv/show/circus_stunts.html.

Here are some additional websites you might want to check out as you start your research:

Short introduction into the physics of tightrope walking:Clark, J., 2000. "Tightrope Walking," Physics of the Circus, Mr. Fizzix Physics website [accessed June 30, 2007] http://physicsofcircus.homestead.com/files/tightrope3.htm.

Explanation on how torque and rotational motion relates to tightrope walking:Clark, J., 2000. "What is Torque?" Physics of the Circus, Mr. Fizzix Physics website [accessed July 2, 2007] http://physicsofcircus.homestead.com/files/torque.htm.

Short explanation of the physics of balancing on a tightrope:Taylor, D., date unknown. "Circus High Wire," Newton's Apple, KTCA Twin Cities Public Television [accessed June 30, 2007] http://www.darylscience.com/Demos/TightRope.html.

Materials and Equipment

To do this experiment you will need the following materials and equipment:

Stop watch or timer that measures seconds

Sidewalk curb with at least 3 meters (approx. 9 feet) clearance on either side An assistant to take times and spot you, if needed Two poles of the same material

o One pole should be at least 2 meters (approx. 6 feet) longer than the other. o You can use wood poles, PVC pipe, or small diameter plumbing pipe.

Notebook Pen or pencil

Experimental Procedure

1. Gather your materials and arrange with your assistant the day and time of your experiment. 2. The day of your experiments, first practice balancing without poles while standing on the edge

of the curb facing the sidewalk. Your heels should not touch the curb. 3. If you find this too easy, balance while slowly raising your heels up and down, or balance on

one foot for your trials. Decide which type of balance test you want to do in your experiments. 4. Prepare a data table similar to the example shown below. 5. Perform the three experiments listed in the table. The first experiment involves balancing while

placing your arms in three different positions. The second and third experiments involve balancing with a short or long pole held close to your body at three different levels. Do five balancing trials for each position in all experiments.

6. Your assistant should record how long, in seconds, you stay on the curb for each trial. 7. Also note how stable you feel while balancing in each position. Record a "wobble rating" for

each position (i.e. slow = steady, medium = less steady, fast = unsteady).

Balancing Experiments Data TableName:   Date:Pole Material:   Location:

Experiment No. & Positions

Balance Time (sec)Wobble Rating

(Slow, Med, Fast)Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Total

Exp 1. Arms Only              

A. Arms down at sides              

B. Arms out to sides, shoulder level              

C. Arms above head              

Exp 2. Short Pole Only              

A. Pole at waist              

B. Pole at shoulder level              

C. Pole above head              

Exp 3. Long Pole Only              

A. Pole at waist              

B. Pole at shoulder level              

C. Pole above head              

Analyzing Your Data

1. Total the seconds for all trials. Calculate an average balance time for each position. 2. Use the three average times within each experiment to calculate a "total average time" for

Experiments 1, 2, and 3. 3. Prepare a bar chart showing the average and "total average" times for Experiments 1, 2, and

3. Group the the data by experiment number so you can more easily compare the results between the three experiments.

4. What positions were best and worst for balancing? Were they the same in all three experiments?

5. Which experiment showed the longest average times? Were you surprised by your results? 6. What did you notice about the speed of wobbles when using no poles, a short pole, or a long

pole? 7. Construct stick figure diagrams to represent your positions in each experiment. Indicate where

you think the center of gravity is located on each stick figure. Hint: Start with the center of gravity at the belly button for Experiment 1A. Then show on other stick figures how the center of gravity moves up or down when the arms or poles are added in the next positions or experiments.

8. What do you notice about the placement of the center of gravity and the number of seconds you could balance in each position?

9. For help with data analysis and setting up tables, see Data Analysis & Graphs. 10. For a guide on how to summarize your results and write conclusions based on your data, see

Conclusions.

Variations

More data. Have your assistant or a few friends try the same experiments. Are the results similiar? If not, try to explain why.

Heavy lifting. Repeat the experiments using two soup cans as weights. Hold them in your hands or duct tape them to the ends of the poles. (You can also use wrapping flexible ankle or wrist weights if you have them.) How does the additional weight affect your results? Adjust your placement of the center of gravity in the stick figures you drew to show how it shifts when weights are involved in each position.

Change your view point. Repeat the experiments with your head turned to the side or with your gaze upward. Be sure to have your assistant close by in case you need a spotter for some of the balancing tests. Compare these results with your results from the original three experiments. How do visual cues help us in balance? Do some research into how the eyes and ears are important for balance.

Stay on the beam. Repeat the experiments using a wooden 2x4 beam nailed into the grass to keep it from wobbling. Record the number of times you can travel up and back. Are your results on balance while traveling along the balance beam similar to the results you got when you balanced while standing on a curb? For an experiment that describes how to make this type of balance beam and includes various tests to try, see "Balancing Act,"http://www.darylscience.com/Demos/TightRope.html.

Baby steps. Research how a baby learns to walk. Investigate the importance of the ratio of the baby's head size to body size during the first couple of years and how the ratio influences center of gravity and the ability to walk.

Do the math. For students interested in mathematical descriptions of balance, look up the equations for torque, angular velocity, and angular acceleration. Calculate the changes in angular acceleration when a tightrope walker of your height wobbles or falls without a pole and then with poles of various lengths.