# Hands-on Activity: Egg-cellent Landing

### Summary

The purpose of this activity is to recreate the classic egg-drop experiment with an analogy to the Mars rover landing. The concept of terminal velocity will be introduced, and students will perform several velocity calculations. Also, students will have to design and build their lander within a pre-determined budget to help reinforce a real-world design scenario.

### Engineering Connection

Through careful design and many experimental trials, engineers have developed ways to safely stop objects moving at high speeds. They incorporate into the design of moving objects — cars, airplanes, trains, amusement park rides, bicycles — components and devices that mitigate the effect of abrupt slow down; for example, bumpers, crumple zones, seat belts, air bags, shock absorbers or helmets.

### Educational Standards

•   Common Core State Standards for Mathematics: Math
•   International Technology and Engineering Educators Association: Technology
•   Next Generation Science Standards: Science

### Pre-Req Knowledge

• Students should understand that objects accelerate as they fall.

### Learning Objectives

After this activity, students should be able to:
• Identify several components of a Mars lander designed by engineers.
• Design and build an egg-lander within a confined budget.
• Define and understand terminal velocity.
• Recognize similarities and differences between their model lander design and the Mars Landing Spacecraft design.

### Materials List

Each group should have:
• One egg
• One Zip-Lock™ (or other "zipper" brand) sandwich bag
For each class:
• Styrofoam or plastic cups
• Low-density foam (available at most fabric stores)
• Pack of balloons

### Introduction/Motivation

Through careful design and many experimental trials, NASA engineers have developed a way to safely land Mars rovers when approaching the great Red Planet at speeds exceeding 12,000 mph. To slow down the spacecraft that is transporting the rover, engineers have designed a craft that includes an aeroshell, which in turn in comprised of a heat shield, a parachute, airbags, rockets and lander , among other important components. Once the heat shield has done its part in effectively bringing the lander to a vertical stop 40 to 50 feet above the ground, the bridle that tethers the lander to the aeroshell's backshell is cut, and the lander — surrounded with airbags and containing the rover inside — free falls to the Martian surface and bounces its way to a stop.
The Egg-cellent Landing activity will simulate the free-falling lander and its subsequent bouncing that occurs before it finally stops. However, since the experiment will be done on Earth and not on Mars, we can take advantage of Earth's thicker atmosphere.
Students should understand that objects accelerate as they fall. However, falling objects experience drag, which is friction caused by the atmosphere. As an object falls faster, drag increases. Eventually, the drag balances out the weight of the object and prevents any further acceleration. The object will then continue to fall at a constant speed known as its terminal velocity. A good visual example of terminal velocity is to drop an inflated balloon, which will fall at a very slow rate.
Fun Fact: Did you know that you cannot kill a mouse by dropping it out of a skyscraper because its terminal velocity is so slow that it will be relatively unharmed when it hits the ground.
Terminal velocity is affected by the aerodynamics and weight of an object. If an object is not aerodynamic, it will experience more drag than an aerodynamic object. Also, a heavier object will have a faster terminal velocity than a lighter object with the same aerodynamics. Finally, the atmosphere and gravity have a secondary affect on terminal velocity since the weight of an object will depend on the gravity, and the drag acting on the object depends on the atmosphere.

### Procedure

Before the Activity

• Gather all necessary materials.
• Make enough copies of the Egg-cellent Lander Order Form for each group to have one copy.
• Designate a testing area with a hard landing surface (i.e., tile or concrete) to drop the student's egg-landers (a balcony, window, or even a ladder work perfectly).

With the Students

The objective of this exercise is for students to design an egg-lander within constraints to keep an egg from breaking when it hits the ground from a significant height. The landers are allowed to bounce when they hit the ground.
1. Challenge each student group to design a safe landing craft for their raw egg.
2. Explain to the students that each group only has \$1 to purchase materials.
3. Pass out one Egg-cellent Lander order form to each group.
4. The groups should sketch their design on their order form before they pick up their materials.
5. Pass out one egg to each group. Have the groups immediately place their egg in a zipper bag to prevent any accidental messes.
6. Allow the groups time to build their egg-landers.
7. Test the egg-landers in the designated area.
8. A group will have successfully completed the mission if their egg remains unbroken after the fall.

### Safety Issues

Be sure to have students wash their hands if they touch any broken egg.
Please do not encourage student to attempt to verify this activity's Fun Fact.

### Troubleshooting Tips

Placing the raw eggs into zipper bags at the start of this activity helps minimize any nasty clean-up when the students drop their landers. When the activity is done, dispose of the eggs into an outside receptacle or a waste bin that will be emptied shortly, since raw eggs do not smell good when left out of refrigeration for a while.

### Assessment

Pre-Activity Assessment

Brainstorming: In small groups, have the students engage in open discussion. Remind students that no idea or suggestion is "silly." All ideas should be respectfully heard. Ask the students:
• Ask the students to come up with some ideas on how to safely land a delicate falling object like an egg. (Possible answers may include: padding or foam, airbags or balloons, springs, parachutes, etc.).
• What two types of engineers would most likely work on building a lander for a delicate and expensive falling object like a Mars rover? (Answer: aerospace and mechanical engineers)

Activity Embedded Assessment

Velocity Calculation: Calculate an equation, and summarize student responses. Write the correct answer on the board.
• When falling, a balloon will immediately reach its terminal velocity. Drop a fully inflated balloon from 5 feet and record the time it takes to hit the ground. Have the students calculate its terminal velocity by the simple equation,
Velocity = Distance ÷ Time
If it took 3.1 seconds to fall 5 feet, your answer would look like:

Post-Activity Assessment

Show and Tell: Have the students "show and tell" to the rest of the class their egg-cellent landers that they created, explaining their work to the other students.
• Have students explain the best part of their design and what could go wrong with it (and what could be fixed in future models). Remind students that engineers go through the deign/build/redesign process many times before they arrive at a finished product.
Velocity Evaluation: To reinforce the concept of aerodynamics and weight affecting terminal velocity, have the students predict the outcome of the following two cases.
• If the balloon used in the Embedded Assessment was only inflated one-half the amount and still dropped from a 5 ft. height, would it hit the ground in more or less time? Would its terminal velocity be slower or faster? (Answer: The balloon would take less time to hit the ground, and its terminal velocity would be faster. Because the balloon has a smaller area when it is deflated, it will experience less drag.)
• If a coin were taped to the fully inflated balloon to add more weight and dropped from a 5 ft. height, would it hit the ground in more or less time than the inflated balloon without the coin? Would its terminal velocity be slower or faster? (Answer: The balloon would take less time to hit the ground and its terminal velocity would be faster. A heavier item has a faster terminal velocity than a light item of the same aerodynamics.)
Problem Solving: Have the students engage in open discussion to suggest solutions to questions/problems.
• We performed the egg-lander experiment on Earth rather than on Mars where the atmosphere is much thinner. What problem could this present if we tested our designs on Mars? (Answer: Because the atmosphere is so thin, the lander would not come close to reaching its terminal velocity, which is very fast. Instead, it would keep gaining speed while falling until it finally hits the ground.)

### Activity Extensions

Calculate the terminal velocities for the two balloon scenarios in the Velocity Evaluation in the Post-Activity Assessment. Then, compare the results with the Velocity Calculation in the Activity Embedded Assessment.

### Activity Scaling

• Additional materials not listed in the Materials List may be purchased and added to the Egg-cellent Lander Order Form if a more difficult and diverse selection is desired. For example, both large and small balloons could be purchased.
• Prices may be adjusted in the Egg-cellent Lander Order Form to make the design more challenging. For example, balloons could cost twice as much as foam.
• In order to make the terminal velocity harder to reach, do not allow the groups to fully inflate their balloons.

### Contributors

Chris Yakacki, Geoffrey Hill, Daria Kotys-Schwartz, Malinda Schaefer Zarske, Janet Yowell