Rubber Bands for Energy
AbstractIf you have ever been shot with a rubber band then you know it has energy in it, enough energy to smack you in the arm and cause a sting! But just how much energy does a rubber band have? In this experiment you will find out how the stretching of a rubber band affects the amount of energy that springs out of it.
ObjectiveInvestigate how the distance of stretch in a rubber band at rest relates to the distance the rubber band travels after being released.
No mechanical contraption would be any fun to use if it did not work. But to do "work" in the classical sense, takes energy. Consider a rope and pulley that bring a bucket up a well. They would not work at all if there was not a person using their own energy to pull up the rope. The person is providing an energy input for the mechanical system to work.
Clearly mechanical systems need energy to do work, and the energy needed comes in two different kinds:
- Potential Energy (PE): energy that is stored
- Kinetic Energy (KE): energy in motion
A great example of the difference between kinetic and potential energy is from the classic "snake-in-a-can" prank, shown in Figure 1. This is an old joke where you give someone a can of peanuts and tell them to open it, but inside is actually a long spring that jumps out of the can when they open it. Since the spring is usually decorated to look like a long snake, this prank usually causes the victim to jump back and shout! When the snake is secured inside the unopened can, it has potential energy. But when the can is opened, the potential energy is quickly converted to kinetic energy as the snake jumps out of the can!
There are two types of energy being demostrated potential energy (PE) and kinetic energy (KE). Potential energy is energy that is stored. Kinetic energy is energy that is in motion.
Figure 1. The "snake-in-a-can" joke is an example of Potential Energy (PE) and Kinetic Energy (KE). (Image adapted from www.supercoolstuff.com.)
In this science fair project, you will investigate how kinetic and potential energy work in a very simple system: a rubber band shooter. In this system you will stretch a rubber band over the end of a ruler and release it (without aiming it at anyone of course). By stretching the rubber band back to different lengths, you will give the system different amounts of potential energy. Because the rubber band shooter is technically an elastic system, the kind of potential energy that it has is specifically called elastic potential energy. When the rubber band is released, the potential energy is quickly converted to kinetic energy. You will investigate the relationship between the potential energy and kinetic energy in this system by seeing how far the rubber band flies when it is stretched to different lengths. How will the potential and kinetic energy affect the distance your rubber band travels?
Terms and Concepts
- Energy input
- Mechanical system
- Potential energy
- Kinetic energy
- Energy conversion
- Elastic potential energy
- If I stretch it back 30 centimeters (cm), how far will the rubber band go? If I stretch it back to only 10 cm, how far will the rubber band go?
- Which gives the rubber band the most potential energy, stretching it to 30 cm or 10 cm?
- What is the difference between elastic potential energy and other forms of potential energy? What is the mathematical equation for calculating elastic potential energy?
BibliographyThese websites are a good place to start gathering information about potential energy and kinetic energy:
- Rader, A. (n.d.) Energy of Motion. Physics4Kids.com. Retrieved April 5, 2012.
- Wisconsin K-12 Energy Education Program (KEEP). (2002). What is Energy?. Retrieved April 5, 2012.
- UCSB ScienceLine. (n.d.). Does the amount of stretch of a rubber band affect the distance a rubber band will travel?. Retrieved April 3, 2014.
Materials and Equipment
- Metric ruler
- Rubber bands (all of the same size and kind)
- Metric tape measure
- Sidewalk chalk
- Lab notebook
- First write a data table in your lab notebook similar to Table 1.
- On your ruler, you will be pulling rubber bands back to five different stretch lengths: 10 centimeters (cm), 15 cm, 20 cm, 25 cm, or 30 cm. You will measure how far the rubber bands fly when released from the different stretch lengths and then write your results down in the data table in your lab notebook.
|Average Distance (cm)
Table 1. In your lab notebook, write a data table like this one so that you can record how far your rubber bands fly when they are released from different stretch lengths.
- Find a helper, gather your supplies, and go outside to do this experiment. You will want a place with a lot of clearance that has a cement or hard-caped surface that you can draw on with chalk. Your helper will draw circles around where the flying rubber bands land, so choose a helper with a keen eye and some running shoes!
- Stand on one side of the space, and have your helper stand on the other side, not directly in your line of fire!
- With your piece of chalk draw a line in front of your toes. This is where you will line your feet up when you shoot your rubber bands. This is also where you will begin measuring the distances your rubber bands have gone.
- Shoot a rubber band by hooking it on the front edge of the ruler, then pulling back to your first length (10 cm) on the ruler and then letting go.
- Remember the angle and height you hold the ruler, because you will need to keep it the same for each rubber band launch.
- Have your helper draw a circle where that rubber band landed.
- Measure the distance from your line to the spot your helper just marked. Write this measurement in your data table.
- Repeat steps 5 to 7 nine more times. Did all 10 trials have similar launch distances, or was there a lot of variation in how far the rubber bands flew? Average the data from these 10 trials to get better results.
- Repeat steps 5 to 8, but use a different stretch length each time. For example, after you have done 10 trials for the 10 cm stretch length, do 10 trials for the 15 cm stretch length, then the 20 cm stretch length, etc.
- Stop after you have done 10 trials for the five different stretch lengths.
- Be sure to average your results for each stretch length.
- Make a graph of your results.
- You can make a graph by hand or use a website like Create a Graph to make a graph on the computer and print it.
- Put the stretch length (in centimeters) on the bottom (x-axis) and the launch distance (also in centimeters) on the left side (y-axis) of the graph. Plot a dot for the average launch distance (how far the rubber bands flew) of each stretch length.
- Do the dots follow any type of pattern or trend? Does it look like a straight line or does it curve? If it looks like a straight line, draw a line of best fit through your data.
- What was the relationship between the amount of stretch and the launch distance? What do you think this means about the relationship between potential and kinetic energy?
Ask an Expert
- You can do a very similar science project to this one by using other types of mechanical systems, such as springs and sling shots. How do the data collected using these other mechanical systems compare to the data collected using rubber bands?
- In this experiment you kept the angle and height of launch the same from trial to trial. How would these variables affect the distance the rubber band would travel? Design a separate experiment to test each of these variables separately.
- Advanced students can use linear regression to further analyze the data. Can you define an equation that expresses the relationship between potential and kinetic energy in this system? What is the error in your experiment? Are your results significant?
- Knowing the stretch length and the stretch constant of a rubber band, you can calculate the potential energy the rubber band has, which will let you calculate the kinetic energy the rubber band has when you launch it. Knowing its kinetic energy, you can calculate how far the rubber band should travel before hitting the ground. How close are your results to predicted results based on these calculations? If your results are different, why do you think this is? To see how to do these calculations, check out the UCSB ScienceLine resource in the Bibliography in the Rubber Bands for Energy section.
If you like this project, you might enjoy exploring these related careers: