Diving Eggs Inertia Challenge

Introduction

Students experience the effects of inertia every day—riding in a car, playing sports, even when picking up their backpacks. Present a more dramatic demonstration of Newton’s first law by safely and simultaneously dropping three eggs into beakers of water, without touching the eggs! Applause is guaranteed!

Concepts

• Balanced forces
• Inertia
• Newton’s first law of motion

Experiment Overview

The purpose of this activity is to demonstrate Newton’s first law of motion—the law of inertia. Three weighted plastic eggs will be balanced on tubes on a pie plate over three beakers of water. As a net horizontal force is exerted on the pie plate, the eggs will drop into the beakers.

Materials

Safety Precautions

Clean up spills immediately. Wear safety glasses. Observers should be a safe distance away from the trajectory of the pie pan. Wash hands thoroughly with soap and water before leaving the laboratory. Follow all laboratory safety guidelines.

Disposal

All materials may be dried and stored for future use. The clay may be removed from the eggs and stored in a resealable plastic bag.

Prelab Preparation

1. Separate the clay stick into three equal pieces.
   {12157_Preparation_Figure_1}
2. Open one plastic egg and press about two-thirds of one piece of clay into the narrow end of the eggs (see Figure 1).
3. Press the other third of the piece of clay into the wide end.
4. Close the egg, making sure it snaps tightly shut.
5. Repeat steps 2–4 with the other two eggs.

Procedure

1. Obtain three identical beakers or clear drinking glasses. The diameter should be wide enough for an egg to fit in sideways.
2. Fill each beaker about two-thirds full with tap water. If using 400-mL beakers, fill to the 250-mL mark.
3. Place a towel along the edge of the demonstration table and smooth it out across the table.
4. Place two of the beakers on the towel next to the edge of the table. The rim of the beakers should be near, but not extending over, the edge of the table.
5. Place the third beaker between the other two, forming a triangle (see Figure 2).
   {12157_Procedure_Figure_2_Overhead view}
6. Center the pie plate right side up on top of the three beakers. The edge of the pan should extend slightly beyond the edge of the table.
7. Stand the three plastic tubes vertically on the pan, centering one tube over each beaker (see Figure 3).
   {12157_Procedure_Figure_3}
8. Carefully balance one clay-filled plastic egg on top of each tube, laying the egg lengthwise across the top of the tube. Do not fit the narrow end of the egg into the tube; the egg should just rest on top (see Figure 3). Note: If one end of the egg slips into the tube, open the egg and adjust the amount of clay in each end as necessary.
9. Obtain a broom and place the bristles on the floor by the table with the handle extending upward.
10. Holding on to the broom handle and facing the egg setup on top of the table, step on the bristles of the broom with one foot.
11. Pull back on the broom handle like a lever (see Figure 4).
    {12157_Procedure_Figure_4}
12. Without letting go of the broom handle, carefully test to see if the handle will hit the pie pan between the two beakers along the edge of the table when the handle is released. If not, adjust the position of the broom accordingly. The handle should not hit either of the beakers, just the pie pan.
13. While continuing to step on the bristles, pull the broom handle back.
14. Let go of the broom handle and watch as the eggs “dive” safely into the beakers of water.

Student Worksheet PDF

12157_Student.pdf

Teacher Tips

• This kit contains enough materials to perform the demonstration an unlimited number of times: an aluminum pie pan, three plastic tubes, one stick of clay, and six plastic eggs. Extra eggs are included in case of breakage.
• This demonstration may be done as an introduction to Newton’s first law of motion or as a “grand finale” after a unit on force and motion.
• Thin disposable aluminum pie pans may dent with the force of the broom handle, resulting in a less elastic collision. These pans are not recommended for this demonstration. A heavy duty pan is included in this kit.
• If a broom is not available, a quick, strong horizontal slap on the edge of the pie pan with your dominant hand may do the trick.
• Some water may splash out of the beakers. Clean up spills immediately.
• Performing the demonstration without announcement and putting a lot of “flair” into arranging the setup (carefully checking and double-checking the alignment of beakers, pan, tubes and eggs, etc.) greatly adds to the anticipation.
• Videotape the demonstration and then play it back in slow motion.
• Once the instructor is comfortable with the demonstration, add to the suspense by using raw eggs. As long as enough water is in the beakers to cushion the eggs, and everything is set up correctly, the eggs should not break! Note: Be sure to dispose of the eggs in the trash and wash hands thoroughly after handling. Food items brought into the lab should never be eaten.
• Newton’s Laws Activity Stations Kit (Flinn Catalog No. AP7408) may be used to further explore Newton’s laws of motion.

Answers to Questions

1. Draw the setup (see Figure 3).
   {12157_Procedure_Figure_3}
2. Briefly describe the sequence of events in the demonstration.

   The broom handle was pulled back and then released. The handle hit the pie pan, causing it to move horizontally. The plastic tubes toppled over, so they were no longer holding up the eggs, and the eggs fell into the beakers of water.

3. State Newton’s first law of motion.

   An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and direction unless acted on by an unbalanced force.

4. What is inertia? How are mass and inertia related?

   Inertia is the tendency of an object to resist change in motion. Mass and inertia are directly related—the greater the mass of an object, the greater its inertia.

5. Why is Newton’s first law of motion referred to as the law of inertia?

   An object requires a force to change its motion because of its inertia.

6. 1. What balanced forces were acting on the eggs before they fell?

      When the eggs were at rest, the upward force of the tubes and the downward pull of gravity cancelled each other out. With balanced forces acting on the eggs, they remained at rest.

   2. Was a horizontal force applied to the eggs?

      No horizontal force was applied to the eggs, only to the aluminum pan.

   3. Explain why the eggs dropped into the beakers in terms of Newton’s first law of motion and inertia.

      When the horizontal force was applied to the pan, the pan accelerated in the direction of the force. Since the plastic tubes have a relatively small mass, the force of friction between the tubes and the pan was enough to overcome the inertia of the tubes, causing the tubes to topple over. The eggs have greater mass—and thus greater inertia—than the tubes and they briefly remained in place. Once the upward force of the tubes was gone, the force of gravity caused the eggs to drop into the beakers.

Discussion

Newton’s first law of motion states that an object at rest tends to stay at rest unless a net force acts on it. This law is also known as the law of inertia. Inertia is the tendency of an object to resist change in motion. Inertia is directly related to mass—the greater the mass of an object, the greater its inertia. In the Diving Eggs Inertia Challenge setup, all the forces are balanced when all the objects are at rest. A net horizontal force is supplied by the moving broom handle. This force acts upon the aluminum pan, which then accelerates in the direction of the applied force. Since the plastic tubes are lightweight and have little inertia, friction between the pie pan and the plastic tubes causes the bottom of the tubes to move with the pie pan. The unbalanced forces on the plastic tubes cause them to topple over. The eggs do not move with the tubes because of their greater inertia. Since no horizontal force acts on the eggs, once the force holding them up is gone, the only remaining force is gravity, and the eggs drop into the beakers of water. The upward or buoyant force of the water counteracts the acceleration of the eggs due to gravity, preventing them from breaking.