Will the egg break?

- Students will be able to explain why the changes in momentum and the associated impulse used to change momentum are identical when two eggs of identical mass and initial velocity are bought to rest by a wall and by a sheet.

- Students will be able to explain how throwing an egg into a fitted sheet causes increase in time which causes a decrease in force required to bring the egg to rest

Before doing the discrepant event, make sure students have a working understanding of momentum, impulse, and how they are related by the impulse-momentum theorem.

1. Get the students into groups of two. Present these review questions. See student questions (Microsoft Word 30kB Jul30 07) Ask them to work together on these problems. After some time, gather the class together and solicit student answers .

2. Re-derive the impulse/momentum equation by using Newton's Second Law and the linear acceleration equation.

3. Ask for two volunteers and one person to throw an egg. Make a big deal out of getting safety goggles, rain jackets, a mop etc.

4. Before the egg is thrown into the sheet, ask students to individually predict what will happen if an egg is thrown into a sheet. Ask them to hypothesize why they think it will happen. Make sure that this is written down. Have them share this with a partner. Have students share their predictions and reasoning with the class. Encourage them to use physics terms and use drawings.

5. By a show of hands, have students vote if they think that the egg will break. Have the student throw the egg. Slow motion video of this demonstration is available for purchase at http://www.physics.montana.edu/demonstrations/video/1_mechanics/demos/egginsheet.html

6. Have students imagine that an identical egg was thrown at the same speed into the wall. Have them explain to each-other why the egg does not break in the sheet but does in the wall. Solicited a few responses from the class.

7.Guide the students through the following series of questions. For each question have students vote and discuss. See student questions (Microsoft Word 30kB Jul30 07)

8. After this series of questions, guide students to understanding why the egg breaks when it hits the wall but does not when it hits the sheet by using the momentum impulse theorem. See the illustration below. The size of the letters represents the relative sizes of force and time. Do one symbol at a time for the wall and the sheet starting with mass and change in velocity. Reinforce the idea that change in momentum is the same. Move to force by drawing a large force for the wall and a small force for the egg. Ask students what must be true about the relative size of the time in order to have the same changes in momentum. Finally, fill in the time.

9. Ask students to re-explain to each-other how this explains why the egg breaks on the wall but not on the sheet.

student questions (Microsoft Word 30kB Jul30 07)

Make sure that the sheet holders have goggles on and hold the sheet so the egg does not roll out at the bottom.

If an egg breaks and gets on any students , make sure to have students wash hands thoroughly with soap and water.

Conduct informal, formative assessments throughout the review questions and student responses through the demonstration and explanation.

To conduct a more summative assessment, have students complete a ticket to leave. A ticket to leave is a half sheet of paper in which students answer questions on a sheet of paper and hand them to you as they leave the class. See attached questions.

This activity is modified from the "Egg Toss" laboratory investigation found in Conceptual Physical Science Explorations.

High speed photography can by found at Montana Physics Demonstrations