This project involves the design, fabrication and testing of devices that will launch a penny as far as possible along a straight line. The launching system will start at the top of a small ramp and possibly use the ramp to transfer the energy of the movement down the ramp into the launch. Students will design a launching system using common, everyday materials. This project helps students understand some basic principles of dynamics, mechanisms, and simple energy transfer systems. Although the emphasis is on mechanical potential and kinetic energy, many other engineering principles come into play.
The primary purpose of this project is to give students a chance to explore creative solutions to harnessing mechanical energy. They will have an opportunity to build a mechanical device that in some way uses potential and kinetic energy. Students are expected to gain some feel for the principles involved, specifically the conservation of energy principle. Although this project stresses the relationship between kinetic and potential energy, all students can expect some degree of success.
In our world, energy is a limited resource. In many engineering projects, energy cost is significant. Throughout history, designers have tried to efficiently use energy from convenient sources. One of the first recognized mechanical forms of energy was gravitational potential energy. From even before the proverbial apple fell from a tree and hit Newton on the head, engineers have harnessed the force of gravity in designs from the Roman aqueducts to counter-balanced draw bridges.
Even today, engineers use gravitational potential energy in many designs, particularly dynamic mechanical systems, which are mechanisms that move or have moving parts. In dynamic mechanical systems, engineers use what is known as the conservation of energy principle to identify and use relationships between potential and kinetic energy in order to efficiently and effectively harness gravitational force in their creations.
Design, fabrication and testing are all well suited to an indoor site. During design and fabrication, we suggest that each design team have available a flat nine square foot work space. For testing, we suggest a long indoor hallway. The main requirement for a testing site is that it provide adequate length to launch a penny. Typically, no more that 25-feet long and about 10-feet wide are required. It would be a good idea to select a hallway without any obstructions or objects that could conceal a penny after launch.
Time requirements are approximately four hours; however, the project could be done in as little as three hours. If more time is available, then a redesign period of about one hour can be effective. Dividing the total time into approximately hour long segments works well since students will then have an opportunity to discuss and think about possible solutions at home or out of class.
We have found that students can significantly improve their designs with relatively little effort once they start testing their prototypes. For example, raising the height of the penny in their launcher can improve the launch distance.
The following table lists the type and suggested amounts of each material. Given enough notice, you and your students can easily collect these items from home or around school. We suggest that you have each team be responsible for bringing those materials from the list that they wish to use.
Since the material list is simple, students should not require any tools other than scissors, pliers, wire cutters, and rulers.
The suggested size of student teams for this project is from two to three students per team. Your goal when the students are designing their launchers is to have each team member somehow involved. If some team members appear left out, we suggest that you have each team identify specific tasks and responsibilities for each team member. In the student document for this project, we offer some suggestions.
Testing prototype designs is an important step in creating an effective solution to any design problem. Oftentimes, surprising outcomes will occur, and more can be learned about the details of the design problem through prototype testing than from the original design problem statement.
Students, in general, do not take the time to test their prototypes and prefer to call a prototype a completed design. We suggest that you strongly encourage your student teams to test their initial designs, and to further entice them, you might make available an informal prototype test time, where results are not recorded. This will give each team a chance to go through the testing procedure and observe the results of some of their design decisions.
You have two responsibilities in preparing for this project. First, you must build a ramp from which your students will launch their pennies, and second, you must find a suitable testing area. In addition, you will need a tape measure for measuring performance and perhaps some masking tape to mark the test area.
Building A Ramp
The ramp you build should be four feet long, two feet high, and one foot wide. You also should provide a small lip on each side and at the bottom of the ramp. The lip will help prevent designs from falling off the sides of the ramp and will provide a stopping device at the bottom. It is easiest to build the ramp from cardboard, such as that found in typical book or can boxes. Your local grocery store can supply you with plenty of cardboard for this purpose.
First, measure the sides and top for your ramp on the cardboard and then cut out the individual pieces. Remember to measure enough material on the sides to account for the small lip. You will probably need some cardboard for the bottom of the ramp in order to provide the sides with extra stability.
Once you have the top, sides, and bottom cut from the cardboard boxes, you can connect them together using a strong tape or hot glue. We suggest duct tape. When you are taping or gluing the pieces together, remember to provide as smooth a surface as possible for your student's designs to travel down the sloping ramp.
If the ramp seems unstable after having connected all the pieces together, you can also add some cross bracing between the ramp walls inside the ramp box.
Finding a Suitable Testing Area
As previously stated, an ideal testing area would be an indoor hallway about 25 feet long and ten feet wide. The hallway would be free of obstructions that could hinder locating a penny. Hard floors will cause the penny to bounce and roll, but to date, this has not hindered the testing phase of the project.
We feel that giving the students the written material does not, by itself, raise most student's interest in doing the project. Instead, several physical demonstrations presented as a challenge tends to stimulate their interest; however, you are the best judge of what will or will not work with your students.
We suggest a physical demonstration using the ramp that you have built for testing and some projectiles, launched either by hand or rolling them down the ramp. When a penny is rolled down the ramp, it will hit the lip at the bottom and go a very short distance. You might also want to create a simple, weak spring from a paper clip and launch another penny this way. Other demonstrations using the ramp and some projectiles will help get your students interest before you begin discussing what they are supposed to design and build.
We recommend the following approach for managing the project:
Divide the class into design teams of two to three people each and have the teams move such that they are sitting together.
Give a brief demonstration as discussed above, in order to stimulate and challenge your student design teams (5 to 15 minutes).
Distribute the written project materials to each student.
Give the students about 30 to 45 minutes to read the project documents, discuss the principles, and generate design ideas. You might prefer to give a brief presentation about the written materials to the class as a whole.
Give the students any working materials you are providing. Have each team designate one person from each group who is responsible for acquiring those materials. Make sure that each group has a design concept before, they begin building.
Give the students from 60 to 120 minutes to fabricate and test initial designs.
Assign each team a sequence number for formal testing. Since you only have one ramp, each team will need to be ready to test when it is their turn. It is a good idea to test each design more than one time. We suggest three test attempts for each design (3 to 5 minutes per team).
Discuss the results of the testing. Your students will probably have several common designs and some unusual ones. Try to emphasize each team's success, rather than faults.
If you have the time, you can allow for a redesign and retest cycle. Redesign should take less time (30 minutes), but retesting will take the same amount of time.
Once all testing has been completed, spend a few minutes summarizing the results and discussing the primary principle of conservation of energy as related to the class' designs.
Testing the designs is done individually. We suggest that you give each team three attempts on the ramp to launch their penny. Their final EPI would then be the average of each of their attempts. Students typically enjoy the testing phase, when they get a chance top observe the performance of their peers designs. Though most people enjoy friendly competition, try not to emphasize it.
You will need several assistants to help you record and measure results. While the students are discussing and exploring design alternatives, you might want to make up a table on which you can record the testing results.
During testing, you can volunteer some of the students who are not actively involved with their team's testing process to assist you in calling teams to the launch ramp, measuring distance and accuracy, and recording results. Another teacher can also help.
The student document describes a basic performance requirement and an extra performance index (EPI) to measure each design's performance. The EPI allows recognition of superior performance.
The Student Project Description provides a discussion of the conservation of energy principle. Obviously, momentum and projectiles are directly applicable to any launcher design; however, we are attempting to stress energy principles in this project.
Designs that simply move down the ramp and use the ramp's bottom lip to stop the launcher causing the penny to keep traveling are not good performers. To get high performance designs, students will need to not only consider gravitational potential energy but also elastic potential energy from some type of spring launching device. Great designs will use the lip at the bottom of the ramp to "trigger" the spring, which launches the penny. Distances over 15 feet are not uncommon.
Another common design parameter is the height and angle from which the penny gets launched. With sufficient initial velocity, a launch angle of 45-degrees is ideal. The greater the height the penny starts from, the farther it will go.
It is important to note why certain design's were successful. Success in design is primarily attributed to hard work and plenty of testing. True creativity becomes evident by those designs that do not follow the safe course but extend the limits.
If at all possible, try to illustrate and make an example of those designs that did a good job at not only excelling at the performance tests, but also those that were able to harness the different types of mechanical energy as described in the student materials.
Launching projectiles can injure anyone in the path of the projectile. When testing prototypes or final designs, make sure the area out in front of the platform is clear of students or other faculty.
This project was developed by John Garcelon.