Teacher Notes

Rubber Band Cannon

Super Value Laboratory Kit

Materials Included In Kit

Cannon aiming sticks, 8
Cannon bases, 8
Printed Protractor Master*
Rubber bands, thin, 15
Rubber bands, thick, 15
Screws, washers and wing nuts, 8 each
*See Prelab Preparation.

Additional Materials Required

Glue or transparent tape
Metric ruler
Safety glasses or goggles
Scissors
Tape measure

Prelab Preparation

Make enough copies of Printed Protractor Master (see Teacher PDF) for each group.

Safety Precautions

Safety glasses must be worn by everyone during this entire laboratory. Do not aim the Rubber Band Cannon at anyone. The cannon firing should be conducted in an open area such as a gymnasium, cafeteria or outside.

Disposal

All the materials should be saved for future use.

Teacher Tips

  • Enough materials are provided in this kit for 24 students working in groups of three or for eight student groups. All materials are reusable. The laboratory activity can be completed in one 50-minute class period, but several class periods may be needed if additional experiments or contests are performed.
  • The distances the rubber bands travel typically have a wide range. They are significantly affected by air resistance and air currents. Additional trials may be performed for each experiment. Then, high and low values can be ignored when calculating the average values. Several practice launches should also be performed until students are comfortable with a launch technique.
  • The Rubber Band Cannons can be built prior to the lab in order to save time.
  • Since there may be up to eight Rubber Band Cannons in operation at the same time, a large arena will be necessary. Safe areas to fire the cannons include a gymnasium, cafeteria, hallway, empty classroom or outdoors. Determine a suitable location before the laboratory activity.
  • This activity will generate considerable excitement and noise. It might be wise to conduct test-firing in the gymnasium or outside. Inform your colleagues if you are going to perform this activity in the common school hallway so as not to disrupt other classes, especially if the other classes are taking exams. Performing this activity outside the building introduces additional variables including wind direction, wind velocity, temperature, humidity, etc. If the activity is expanded, students may identify additional key variables and design controls to test these variables.
  • In this activity students will fire rubber band projectiles over several meters. Be sure that all safety precautions are followed during this activity. Safety glasses or goggles must be worn at all times by everyone in the area of the Rubber Band Cannons.
  • The key idea of student experimentation is to learn to identify and control variables one at a time so that cause and effect can be inferred. This is the basis of the scientific method. Emphasize this throughout the activity.
  • If students are interested in learning more about how to predict projectile ranges, refer them to any physical science or physics textbook, or the Internet, such as http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html (accessed October 2011).
  • If the room is large enough, use four launch positions at the center of the room, separated by 5 or more feet, with two groups at each position. The two groups at each launch position will fire their cannons in opposite directions so that four of the groups will fire one way and four groups will fire in the completely opposite direction. This should help to optimize the available space and improve safety.

Further Extensions

  1. Predict a combination of variables that will allow the Rubber Band Cannon to hit a target four meters away. Test your prediction. Is there more than one way to shoot the rubber band this distance?
  2. Prepare a “firing table” that shows how different variable combinations may work best for different distances. Test the firing table.
  3. Set up a contest to determine the most accurate firing table. The range officer (teacher) will set up a firing line and a target distance. The target will be a 25-cm diameter circle.

    Rules:

    • Each group has three warm-up shots and three official shots.
    • The target will be placed on the floor two to four meters away from the firing line, but only the range officer will know the distance before the contest begins.
    • The group who hits the target with the most shots is the winner.
    • If there is a tie, the target distance will be changed and the groups that are tied will have a shoot-out.
  4. How did the firing table help in predicting the proper variable values needed to hit the target? How could the firing table be improved? Were there other variables that were not included in the firing table that may have helped to hit the target more often?

Correlation to Next Generation Science Standards (NGSS)

Science & Engineering Practices

Planning and carrying out investigations
Analyzing and interpreting data
Using mathematics and computational thinking

Disciplinary Core Ideas

MS-PS2.A: Forces and Motion
HS-PS2.A: Forces and Motion
HS-PS3.A: Definitions of Energy

Crosscutting Concepts

Scale, proportion, and quantity
Energy and matter
Structure and function
Stability and change

Sample Data

Angle Variable

{13954_Data_Table_1}
Stretch Variable
{13954_Data_Table_2}
Rubber Band Variable
{13954_Data_Table_3}

Answers to Questions

  1. How does changing the angle variable affect the distance of the shot?

    As the angle increases, the distance the rubber band travels also increases up to a point. The maximum distance is achieved at an angle of 45°.

  2. How does changing the stretch variable affect the distance of the shot?

    The more the rubber band is stretched, the longer the rubber band travels.

  3. How does changing the rubber band variable affect the distance of the shot?

    The thin rubber band travels farther than the thick rubber band. This is true when both are stretched a short distance and when they are both stretched a long distance.

  4. Why do you believe one rubber band traveled a greater distance than the other (all other variables being constant)?

    The thicker rubber band did not travel as far as the thinner rubber band. This may be the result of increased air resistance on the thicker rubber band. The air resistance slowed down the thicker rubber band more quickly than the thin rubber band. It was observed that the thick rubber band tended to travel a certain distance and then appear to just fall straight down. The thin rubber band traveled in a more curved path. Also, the thin rubber band seemed harder to stretch than the thick rubber band. So at the same stretch distance, the thin rubber band will supply more force (thrust) as it relaxes back to its original shape. Therefore, the thin rubber band had a faster launch speed than the thick rubber band.

  5. What other variables could be tested that might affect the range of the rubber band cannon?

    Wind or air currents affected the path of the rubber band. The difference between the initial length of the rubber band and the stretched length could be tested. The height the rubber band is actually launched at is also a variable that was not tested.

  6. How might the rubber band cannon improve its range?

    A smoother release mechanism might help improve the accuracy of the Rubber Band Cannon. The rubber band has a tendency to get hung up on fingertips as well as on the launch stick. Thinner rubber bands tend to fly farther which may be the result of less air resistance, so even thinner rubber bands may fly farther.

    Sample Firing Table
    {13954_Answers_Table_4}

Teacher Handouts

13954_Teacher1.pdf

Student Pages

Rubber Band Cannon

Introduction

What determines how far a cannonball will fly? How does the angle of the cannon affect its range? Explore some of the variables that affect projectile motion using a Rubber Band Cannon.

Concepts

  • Scientific method
  • Controls
  • Projectile motion
  • Variables
  • Hooke’s law

Background

When forces are applied to an object, the dimensions of the object tend to change. For example, if opposing forces are applied to both ends of a spring, it stretches or compresses. When the forces are removed, the spring returns to its original length. If an object returns to its original dimensions after the applied force is removed, the object is considered elastic.

The British scientist Robert Hooke (1635–1703) was one of the first to study the elasticity of matter. In 1678, he published his now famous statement of Hooke’s law: The amount of deformation of an elastic object is proportional to the forces applied to deform it.

The stretching of a rubber band and its release is an example of an elastic object that can be deformed to varying degrees. When the applied forces are removed, the rubber band quickly and dramatically returns to its original size. Newton’s third law of motion states that forces always exist in pairs (for every action there is an equal and opposite reaction). When the stretching forces at the other end of the rubber band are removed, the restoring force of the rubber band, anchored at one end, results in the rubber band being shot into the air. The simple stretching and releasing of a rubber band illustrates a number of physical science principles.

Several factors affect how far a projectile will travel. The two most important factors are the launch angle and the strength of the initial push or pull that sets the object in motion. In order to determine how each factor, or variable, affects the projectile firing distance, experiments need to be designed in such a way that the effects of different variables can be studied independently. This is done by making observations under controlled conditions where only one variable at a time is changed. Controlled experiments make it possible to separate or isolate the factors that are responsible for a given observation in a complex series of events.

Materials

Cannon aiming stick*
Cannon base, 8*
Glue or transparent tape
Metric ruler
Protractor cutout*
Rubber bands, 2 (thick and thin)*
Rubber Band Cannon Record Sheet
Scissors
Screw, washer, and wing nut
Tape measure
*Materials included in kit.

Prelab Questions

Preparing the Experiments

Several variables will affect the distance the rubber band will fly. To determine the effect of each variable on the distance the cannon fires, it is essential to change only one variable at a time. Consider these three variables:

  1. The angle of the aiming stick (angle variable).
  2. The amount of stretch to the rubber band (stretch variable).
  3. The length and thickness of the rubber band (rubber band variable).
Fill in appropriate test values for each variable on the Rubber Band Cannon Record Sheet to indicate the experiment tests you will perform to analyze the three variables. Four trials should be performed for each test. The control values for three tests are provided. Additional tests should be used as needed for further analysis of the variable being tested. Remember to change only one variable at a time while keeping the other two variables the same. The distance of each shot will be measured and recorded with each experimental trial.

Safety Precautions

Wear safety glasses or goggles during this experiment. Do not aim the Rubber Band Cannon at anyone. Cannon firing should be performed only in the area specified by your instructor.

Procedure

Building the Rubber Band Cannon 

  1. Cut out the paper protractor.
  2. Secure the paper protractor to the cannon base withglue or transparent tape as shown in Figure 1. Make sure the intersection of the 90° and 0° lines (A) on the paper protractor cutout is placed over the hole in the cannon base and that the edges of the cutout are parallel with the sides of the cannon base.
    {13954_Procedure_Figure_1}
  3. Use a metric ruler to mark lines 1 cm apart on the aiming stick starting from the notched end. Label those marks 1–15 (see Figure 2). Do not mark beyond 15 cm.
    {13954_Procedure_Figure_2}
  4. Poke a hole through the paper protractor cutout with a sharp pencil at the 90° and 0° line intersection so that the hole in the paper is lined up with the hole in the cannon base.
  5. Attach the aiming stick to the block of wood with the screw, washer and wing nut as shown in Figure 3.
    {13954_Procedure_Figure_3}

How to Use the Rubber Band Cannon 

  1. Loosen the wing nut on the cannon base so that the aiming stick swings freely.
  2. Line up the appropriate angle on the protractor sheet with the hole in the aiming stick as shown in Figure 4.
    {13954_Procedure_Figure_4}
  3. Tighten the wing nut to secure the aiming stick at the proper angle.

Firing the Cannon
Caution: Do not fire the cannon in the classroom unless approved by your instructor. Only fire the cannon in an area designated by your instructor. Wear safety glasses. 

  1. Hold down the Rubber Band Cannon base with one hand.
  2. Figure 5 illustrates one manner in which to fire the Rubber Band Cannon. Pull the rubber band to the appropriate stretch distance. Once the end of the rubber band is at the appropriate release length, pinch the very end of the rubber band between the thumb and index finger. Quickly release the rubber band to launch it from the Rubber Band Cannon.
    {13954_Procedure_Figure_5}
  3. One lab partner should fire the cannon while the other partner becomes the spotter to determine the position where the rubber band lands and to measure the distance fired.
Experiment
  1. Perform each test as indicated on the Rubber Band Cannon Record Sheet.
  2. Several practice shots should be made before each test to get a general idea of where the rubber band will land. Misfires, shots in which the rubber band rolls before coming to a stop, or shots that do not have a straight path should be disregarded.
  3. After each trial use a tape measure to measure the distance from the front of the rubber band to the front of the cannon base. Measure to the nearest 1 cm. Record this value in the Rubber Band Cannon Record Sheet in the appropriate space. Perform four trials for each test.
  4. Calculate the average distance the rubber band flew for each test. Record all the information in the appropriate space on the Rubber Band Cannon Record Sheet.
  5. Answer the questions on the Rubber Band Cannon Worksheet after completing the necessary trials for each variable.

Student Worksheet PDF

13954_Student1.pdf

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