Ramp Launcher Design Student Materials

WHY DOES THIS PROJECT MATTER?

Understanding and harnessing energy is an important aspect in many fields in engineering, particularly mechanical engineering. This project gives you an opportunity to design a system that uses different types of energy and the relationship between them to launch a small mass. This relationship is one of the great principles of science, the conservation of energy principle.

This project helps you understand and use two types of energy that many mechanisms and devices use in our day to day lives. The types of energy you will employ in your design are potential and kinetic energy. Many important engineering theorems and laws find their basis in the conservation of energy principle. By designing a launching system that effectively uses both potential and kinetic energy, you will learn about the basic relationship behind the conservation of energy principle, about potential and kinetic energy, and about dynamic mechanisms (devices that move).

Of course, since design requires knowledge of many subjects, you cannot solely concentrate on this principle, but you and your team must effectively incorporate it into your design in order to achieve maximum results. You may also find that relatively simple, minor modifications to your design can significantly increase its performance.

WHAT ARE WE SUPPOSED TO DO?

What you and your team must do is to design a device that launches a small mass as far and straight as possible from a ramp. Your design will start at the top of the ramp, which is four feet long, one foot high, and one foot wide. The ramp has a small "lip" at the bottom. The small mass that you will launch is a penny; therefore, your design must be able to securely hold the penny in the launching system until launch time.

The length of the ramp you will be launching from is a little over four feet long and one foot wide. There is no limit to the height of your launcher, but the length is limited to two feet, and the width of the ramp constrains your design's width to one foot.

You and your team will have four hours to design, build, and test your launching system. It is a good idea to try different configurations before official testing begins. It is also a good idea that your team discuss the various principles involved, and how your design harnesses potential and kinetic energy before you begin building.

Once your team has agreed on a design concept, each member of your team should have some responsibility. Some ideas for team member responsibilities are:

• material procurement,

• penny holder design,

• the body/platform design,

• potential energy expert,

• kinetic energy expert.

Regardless of what roles each team member plays, it is important that everyone is involved and each person's expertise is utilized. If you do not understand what potential and kinetic energy are, then this project gives you an opportunity to become an "expert" by exploring these topics during your design process.

WHAT EQUIPMENT AND MATERIALS CAN WE USE?

You can build your ramp launcher design using any tools and equipment you need. Your system can be made from any of the following materials:

• cardboard (any type, thick or thin),

• aluminum and tin cans (empty or sealed full cans),

• notebook or similar type paper,

• metal wire clothes hangers,

• metal paper clips,

• Scotch type tape,

• plastic straws,

• plastic soda bottles and milk jugs,

• glue.

You will typically have scissors, pliers, wire cutters, and rulers available as tools.

HOW WILL WE KNOW HOW WELL WE HAVE SUCCEEDED?

The Basic Performance Requirement for your ramp launcher design is that it launch the beyond the end of the ramp. An Extra Performance Index (EPI) will be calculated for your design taking into account the distance the penny traveled from the end of the ramp and how far from the centerline of the ramp that penny lands. Your design's EPI is calculated using the formula:

WHAT ELSE MIGHT BE USEFUL TO KNOW?

Energy can be transformed from one kind to another, but it cannot be created or destroyed; the total energy is constant.

The sentence above clearly and concisely states the conservation of energy principle. In this design project we focus on potential and kinetic energy and transforming potential and kinetic energy.

The potential energy of a system represents a form of stored energy that can be converted to kinetic energy. But what is potential energy? Can we see it or feel it? Will it hurt? Consider a mass some height above the floor. As long as we hold the mass in our hands, we restrain the mass from falling, but it has the potential to fall. The ability of the mass to fall to the floor is caused by gravity. In the example below, the potential or stored energy in the mass is directly related to the gravitational force of the mass. We will call this type of potential energy, gravitational potential energy.

If we place the mass on the floor, then the mass has no potential to fall to the floor; therefore, the height of the mass above the floor must come into the equation at some point. From calculus, we can derive the equation for gravitational potential energy as,

where, PE is the gravitational potential energy, m is the mass of the object, g is the acceleration of gravity, and y is the height of the object above the floor. There are several other types of potential energy such as the potential energy of a spring, which we will call elastic potential energy. Elastic potential energy can be calculated using,

where, PE is the elastic potential energy, k is the stiffness of the spring and x is the distance that the spring is stretched or compressed. The more we stretch or compress a spring the more force the spring will exert against us and more potential energy will be stored in the spring. Thus, we can see that just as gravitational force is directly related to gravitational potential energy; spring force is related to elastic potential energy.

Gravitational and elastic potential energies are two types of mechanical potential energy, but what about kinetic energy? Where does it come from and what does it represent? Simply put, any mass that is moving has kinetic energy, which is given by the following relationship,

where, KE is the kinetic energy of the object, m is the mass of the object, and v is the velocity of the object.

Going back to the conservation of energy principle, the total energy of a system is constant, or in other words, the potential energy (PE) plus the kinetic energy (KE) of a system is the total mechanical energy (E) that a system possesses,

It is important to note that we are not normally concerned with the value of the total mechanical energy of a system (E), but that this value does not change during the motion being considered!

Now that we have some idea of the characteristics of potential and kinetic energy, how can we use these concepts in our design? Perhaps some examples of conservation of energy principles will help.

First, let us consider a mass on a sloped ramp like the one you will be using. If we can assume that any friction between the ramp surface and the mass that will travel down the ramp's slope is negligible, then energy is observed and we can relate the energy of the object at the top of the ramp to the energy of the object at the bottom of the ramp by equating the energy:

In terms of the object's mass, initial velocity at the top, ending velocity at the bottom, height at the top, and height at the bottom, we can write using the previous definitions of PE and KE,

If the object is at rest at the top (), and the ramp bottom rests on the floor (), then we can determine what the velocity of the object at the bottom of the ramp to be,

So, we can see that the velocity of the object at the bottom of the ramp depends on the height of the ramp and is independent of the mass of the object traveling down the ramp, given our assumptions.

Now, let us consider a compressed spring with a penny put against the spring. Remember that a compressed spring stores elastic potential energy and that if we released the spring's trigger, then that potential energy will be converted into the kinetic energy by moving the penny with some velocity. From the conservation of energy principle,

Solving for the velocity of the penny,

In these examples, why are we so concerned with the velocity of the penny? We will answer this by asking another question for you to think about; given two pennies with different initial velocities in the same situation, which do you expect to travel farther? You will obviously notice that in the discussion about conservation of energy, we have not directly discussed a system that launches a penny or any other mass. This design task is for you and your team to explore. We, hopefully, have given you some ideas through this discussion on how potential and kinetic energy and the conservation of energy might help you create an innovative solution to the given design task. In your actual solution, there may be more physical principles involved than just conservation of energy.

SAFETY CONSIDERATIONS

Be careful when using pliers since it is very easy to pinch fingers with them. Whenever you use tools that cut objects, you must remember that your fingers or those of class members can be accidentally cut, so use extra caution with the scissors and wire cutters. Depending on the wire cutters you use to cut wire coat hangers, cutting can require some strength and leverage that may put fingers and other items in danger of being cut. If you are having trouble cutting the wire coat hangers, ask for help from your teacher.