Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Add approximately 200 g of sand to each weighing dish for each zip line setup. Enough sand is included for 15 groups.
2. Set up a sample zip line for students to observe and use as a model.

Safety Precautions

Remind students to wash their hands thoroughly with soap and water before leaving the laboratory.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. This laboratory activity can reasonably be completed in one 50-minute class period. The prelaboratory assignment may be completed before coming to lab, and the data compilation and calculations may be completed the day after the lab.
• The following issues may arise while the students are designing their cups. Included are possible solutions.
  • Cup goes down the zip line slowly: Check that the cup slides freely and also check the steepness of the zip line.
  • The remote release line is too short: Have students estimate where the drop should happen and make the string at least that long.
  • The marble does not eject cleanly: Enlarge the opening or unblock the platform. Students can tape pieces of an index card to create a path for the marble to follow.
  • The marble falls out of cup or off platform before remote release: Adjust the tilt of the cup with the string and paper clips or add a ledge to hold the marble in place using a piece of an index card.
  • The marble misses the target: Check that the opening or platform does not interfere with the marble, adjust the length of the remote release and make sure the weighing dish and sand are directly under the string. Remind students to account for the forward horizontal motion of the marble (projectile motion).
  • When performing sample data trials, the most successful drops into the sand were when the remote release was attached to the wall. This made the release distance the same for each drop, which improved the accuracy by removing the human error of reaction time.

Further Extensions

Possible extensions include:

• Have the students design their own marble dropping contraption from household items.
• Increase the steepness of the zip line.
• Challenge students to drop more than one marble at a time onto the target.
• Decrease the size of the target or require a particular target within the weighing dish.
• Provide the students with a different sized cup; alter the item being dropped (e.g., heavier, lighter, irregular shape).

Answers to Prelab Questions

1. Describe how you will modify the cup to hold and release the marble.

   Student answers will vary. Look for modifications that include creating an opening for the marble to roll out of, a platform that drops the marble or method of carrying the marble underneath the cup and dropping it.

2. How will projectile motion affect when the marble is released from the cup?

   The marble will need to be released prior to being positioned over the target because it will follow a curved/parabolic path when released. The marble will have horizontal motion from the cup moving down the zip line and once the remote release is triggered, gravity will cause vertical motion.

3. How fast would a ball be moving after 4 seconds during a free fall drop, neglecting air resistance?

   The ball will be moving 9.8 m/s each second. So after 4 seconds, it would have a speed of 39.2 m/s. (4s x 9.8 m/s²).

Sample Data

Observations

Data Table

* Second set of data was after implementing student hints.

Answers to Questions

1. Explain, in detail, how well your initial design held the marble as it moved down the zip line.

   Student answers will vary.

2. What modifications were made in order for the cup to hold the marble successfully?

   Student answers may include the addition of a lip to hold the marble in place while moving down the zip line to prevent the marble from falling out early.

3. When aiming for the target, which part(s) of your design were the most important for accuracy?

   Answers may include timing and length of the remote release to eject the marble onto the target or a modification to the cup where the marble was held to release the marble cleanly.

4. When testing the remote release, what problems were encountered?

   Determining what length the marble should be at when released from the cup. The length will vary based on the cup modifications. During sample testing, it was discovered that having the remote release secured to the wall at the determined length removed human error in pulling at the correct time.

5. What was the success rate for the modified cup? Use the data table.

   Student answers will vary. For the first set of data, five successful drops and five unsuccessful drops equates to a 50% success rate. After student hints were implemented, a 100% success rate was achieved.

6. Explain the engineering design process used in this activity.

   Student answers should include the concept of making improvements to the design based on testing. Changes and modifications are made to the design after test runs.

7. Describe the motion of the marble after it was ejected from the cup.

   When the marble is ejected from the cup, it continues to move horizontally while adding a vertical component due to gravity. These two components together result in a curved path recognized as projectile motion.

8. How did this activity demonstrate Newton’s first law of motion?

   Newton’s first law states that an object in motion continues in that motion unless it is acted on by a force. In this example, the marble accelerates while traveling down the zip line with the cup. Once the remote release is triggered, the force of gravity acts on the marble, accelerating it toward the ground. Also, when the marble hits the sand, its motion is changed again or stopped.

References

NASA. https://www.nasa.gov/pdf/418005main_OTM_On_Target.pdf (accessed August 3, 2015).

Introduction

How difficult would it be to drop an object out of a moving vehicle and have it land on a specific target? This is how packages are delivered during times of war or natural disaster when land access is limited. Air dropping packages was developed during World War II to send supplies to inaccessible troops. Items dropped included food, medical supplies, weapons and even vehicles, such as tanks. A common type of drop is called a free fall, where there are no parachutes. Design an apparatus that will air drop a small object by free-fall.

Concepts

• Acceleration
• Projectile motion
• Newton’s first law

Background

During an airdrop, an object is carried by a forward-moving device, such as a plane. Acceleration is the rate of change in velocity—an object’s speed and direction. If the speed, direction or both change, then the object is accelerating. Acceleration is a vector, meaning there is both a magnitude and direction of motion. While the object is being carried by the forward-moving device at a constant speed, there is no acceleration in the horizontal or vertical direction. However, there is velocity in the horizontal direction which is equal to the velocity of the forward-moving vehicle. The object begins to free-fall upon release from the vehicle. During free-fall, gravity is the only force acting on the object. Gravity causes the vertical velocity to increase and the object accelerates toward the ground, velocity in the horizontal direction remains unchanged as no force is acting on the object in the horizontal direction (neglecting air friction).

As the object free-falls, it is now a projectile and will follow a path described as projectile motion. A projectile is any object propelled through the air under the influence of a single force. When a projectile has a horizontal component to its motion it will follow a curved path known as projectile motion. The curved path is created by the combination of initial velocity forward—the horizontal component—and the downward pull of gravity—the vertical component (see Figure 1). The vertical motion is due to the acceleration caused by gravity and the horizontal motion arises from Newton’s first law of motion.

Newton’s first law of motion, also known as the law of inertia, states that the motion of an object does not change as long as the net force acting on the object is zero. Another way to state it is, an object at rest stays at rest unless a net force acts on the object, and an object in motion remains in motion with the same speed and direction unless a net force acts upon it. Inertia is the tendency of an object to resist a change in its motion. The object’s acceleration will increase in the vertical direction due to gravity, however, since no force is acting on the object in the horizontal direction, once it is in free-fall, the horizontal velocity remains constant.

Experiment Overview

The purpose of this activity is to modify a cup to carry a marble down a zip line and release the marble onto a target. Utilizing the engineering design process—improving a design based on testing—the initial design will be tested and modifications then made to improve its performance. Important questions to consider when preparing the cup for an airdrop include: How will you modify the cup so it can carry the marble? How will you drop it? What science concepts will help you prepare for this challenge?

Materials

Prelab Questions

1. Describe how you will modify the cup to hold and release the marble.
2. How will projectile motion affect when the marble is released from the cup?
3. How fast would a ball be moving after 4 seconds during a free fall drop, neglecting air resistance?

Safety Precautions

Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

1. Set up the zip line by using 3 meters of fishing line and tying it to two objects (e.g., two chairs or a chair and table). Make sure the line is tied tight and that one side is 50 cm below the other. The fishing line should span a distance of at least 2 meters (see Figure 2).
   {14065_Procedure_Figure_2}
2. Fill the weighing dish with 200 g of sand and place it under the zip line about 0.5 m from the lowest point on the zip line. Using masking tape, mark the position of the target on the floor. It is possible the target will move with trials.
3. Using the materials at the lab station, alter the paper cup so it attaches to the zip line and is able to carry the marble.
4. Fill in the row labeled “Initial” with the appropriate details on the Drop Zone Worksheet.
5. Test your design on the zip line.
6. Add a remote release to the paper cup so it releases the marble at the correct moment, landing in the target.
7. Continue to modify your paper cup and remote release until you accurately hit the target.
8. Keep track of the modifications made in the row labeled “Modified” on the worksheet.
9. Once you finalize the design, fill in the row labeled “Final” on the worksheet.
10. Using the final design, record 10 trials without any modifications and determine the success of the design. Fill in the data table on the worksheet.

Hints:

1. Make sure cup is facing the target and steady before sending it down the zip line.
2. Smooth sand after each trial.
3. Adjust target to be between taped markers after each trial.

Student Worksheet PDF

14065_Student1.pdf