Back and Forth to Go Forward: A Snake on Wheels?
AbstractHave you ever ridden on a Roller Racer® or PlasmaCar®? These are ride-on toys that you move ahead by moving the steering mechanism back and forth. You've probably seen skateboarders "slaloming" on level ground to keep rolling, it's basically the same idea. This project explores the physics behind this method of locomotion.
- Andrew Olson, PhD, Science Buddies
- Roller Racer is a registered trademark of Mason Corporation.
- PlasmaCar is a registered trademark of PlaSmart Inc.
- Morris, S. (n.d.). The Physics of the Roller Racer and the Plasma Car The Experimental Nonlinear Physics Group, Dept. of Physics, University of Toronto. Retrieved May 12, 2014.
ObjectiveThe goal of this project is to study the physics of ride-on toys (e.g., Roller Racers, PlasmaCars) that are powered by moving handlebars back and forth in order to lever the drive wheels from side to side. What is the relationship between frequency of handlebar motion and forward speed?
The Roller Racer and PlasmaCar are ride-on toys that are powered by back-and-forth motion of a steering column connected to the front wheels (see still pictures of each vehicle).
Illustrations of the PlasmaCar and Roller Racer. Note position of the drive wheels behind the axis of the steering column.
Examine the pictures closely, and you'll see that the drive wheels are located behind the axis of the steering column. With this design, the side-to-side motion of the steering column can impart a forward force on the vehicle. Imagine looking down on one of the vehicles from the top, with the steering wheel turned to the right. In this position, the drive wheels are on the left side of the vehicle's center axis. As the steering wheel is turned back to the left, the drive wheels experience a torque, as well as friction with the floor. By Newton's third law of motion, the floor pushes back on the wheels, and a component of the torquing force is translated into forward motion of the vehicle.
Here is a video where you can see the vehicles in action.
There is a knack to getting moving with one of these vehicles, but it is easy to learn. The goal of this project is to determine the relationship between the frequency of steering column oscillation and forward speed of the vehicle. Or, putting it another way, how rapidly should you rock the steering wheel in order to move forward the fastest?
Terms and ConceptsTo do this project, you should do research that enables you to understand the following terms and concepts:
- Newton's laws of motion
- How are the forces that move these vehicles similar to those involved in snake locomotion?
- Morris, S. (n.d.). The Physics of the Roller Racer and the Plasma Car. The Experimental Nonlinear Physics Group, Dept. of Physics, University of Toronto. Retrieved May 12, 2014, from http://www.physics.utoronto.ca/~smorris/edl/plasmacar/plasmacar.html
- Nice, K. (n.d.). How Force, Power, Torque and Energy Work. HowStuffWorks.com. Retrieved May 12, 2014, from http://science.howstuffworks.com/fpte.htm/printable
- This website about forces is aimed at upper middle school grades:
Rader, A. (n.d.). Motion: Forces. Physics4Kids.com. Retrieved May 12, 2014, from http://www.physics4kids.com/files/motion_force.html
- Here is a high-school level tutorial on Newton's laws of motion:
The Physics Classroom. (n.d.). Newton's Laws. Retrieved May 12, 2014, from http://www.physicsclassroom.com/Physics-Tutorial/Newton-s-Laws
- Mason Corporation. (2012, September 11). Roller Racer® Sport - The Heavy-Duty Sit-Skate. Retrieved May 12, 2014, from https://www.youtube.com/watch?v=pOtAW1QYGD8
Materials and EquipmentTo do this experiment you will need the following materials and equipment:
- Vehicle powered by side-to-side motion, such as
- The Roller Racer, available from Amazon.com
- The PlasmaCar, available from Amazon.com
- Smooth, level surface for riding
- Helpers to time you (1-2)
Note: in theory, it should be possible to adapt this project to a skateboard, but it requires considerably more skill to make the required motions and to be able to do them consistently enough for a controlled experiment.
- First do your background research, and make sure that you understand the terms and concepts above.
- For this project, you'll be running a series of time trials over the same straight and level course. You should mark off a starting line, a finish line and measure the distance between them.
- Your helper says "go" and starts the stop watch.
- At the same instant, you start moving on the vehicle, keeping up a steady back-and-forth rhythm. (If you have a metronome, you could use it to help keep a steady rhythm.)
- You count the number of back-and-forth cycles you make (each time you move the steering mechanism from one side to other and back again counts as one cycle).
- Your helper stops the stopwatch and calls out "stop" (so you know exactly when to stop counting) when you cross the finish line.
- Your average speed will be the distance of the course (in meters or feet) divided by your time (in seconds).
- Your average frequency will be the number of cycles you counted divided by your time (in seconds).
- Repeat steps 3–6 at least five times at one steady frequency.
- Try at least two different faster frequencies and at least two different slower frequencies, again, five trials for each (minimum 25 trials total).
- Does forward speed increase with rocking frequency, or does rocking faster become counterproductive at some point? Why?
- Graph your average speed vs. rocking frequency.
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- For more detailed analysis of your velocity and acceleration, you will want to include some intermediate points on your course, at known distances from the starting line. As you pass each point, you will call out the number of cycles you've counted up until then, and your helper with the watch will call out the time. You will be able to calculate the average speed and your rocking between each point on the course. This will give you information about how steadily you are maintaining the pace, and how your speed is changing as you go. You may find that you need a second helper to record the additional data that will result. Your analysis should include your speed and rocking frequency at the intermediate points, as well as the average for the whole course. Were you able to keep up a steady pace? How do the results compare to riding while sitting straight?
- You could also use a video camera (preferably with an in-frame timer recorded along with the video) to record your motion along the course. On playback, you'll be able to analyze your frequency, and the times you pass the marked points on the course.
- Does the best frequency vary or stay the same for riders of different weights? Design an experiment to test your hypothesis.
- What additional forces would be imparted by rocking your body from side to side in synchrony with the steering mechanism? Would you expect these forces to increase, decrease, or have no effect on forward speed? How about rocking in anti-phase with the steering mechanism? Design an experiment to test your hypothesis.
- Analyze the forces that should be applied in order to direct the vehicle along a circular path. From your analysis, predict whether top speed along a circular path will be equal to, lesser than, or greater than top speed along a straight path? Does your analysis work in practice?
- For a more advanced project, determine the efficiency of this method of locomotion. How much of the energy put into the system goes into forward motion? Where does the rest of the energy go? Compare to locomotion of a snake.
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