Education.com
Try
Brainzy
Try
Plus

# Supporters: How Does the Molecular Structure of an Eggshell Affect its Strength?

based on 12 ratings
Source:
Author: Janice VanCleave

### Problem

How does the molecular structure of an eggshell affect its strength?

### Materials

• Metal spoon
• 4 raw eggs in their shells
• Bowl
• Tap water
• Paper towel
• Nail scissors
• Several books
• Bathroom scale

CAUTION: Always wash your hands after touching an uncooked egg. It may contain harmful bacteria.

### Procedure

1. Using the edge of the spoon, carefully break off the small end of each eggshell. If any cracks form up the side of a shell, discard it and use another egg.
2. Shake out the contents of each egg into the bowl.
3. Rinse the inside of the eggshells with water.
4. Carefully dry the outside of the shells with the paper towel.
5. Wrap a piece of tape around the center of each shell as shown, positioning the tape the same on each shell.
6. Use the nail scissors to cut away the broken ends around the bottom of the tape on each shell.
7. Place the shells, open end down, in a rectangular array on a table.
8. Place one book on top of the shells, and position the shells so that one is under each corner of the book.
9. Carefully add the other books, one at a time, to the book on top of the eggshells, waiting 30 seconds before adding each book. Keep adding books until a cracking sound is heard. Record the number of books required to cause the first crack.
10. Continue to carefully stack the books until one or more of the shells collapse. Record the number of books required to cause the crush.
11. Use the bathroom scale to weigh first the books required to crack a shell and then all of the books required to collapse one or more of the shells.

### Results

The number of books the eggs will hold depends on the weight of each book and the shape of the eggs used. [The author's result was that 5 books weighing 15 pounds (6.8 kg) produced the first crack, and 2 additional, smaller books, bringing the total weight to 19 pounds (8.6 kg), collapsed the eggs.]

### Why?

Eggshells consist largely of the mineral calcium carbonate. The molecules of calcium carbonate are arranged in a dome-shaped structure around the contents of the egg. The weight placed on top of each egg is spread down along the curved sides to the base. No single point on the dome supports the whole weight, so together they can support quite a heavy weight. The dome shape provides a structure imitated by architects because of its strength and ability to span a large area.

### Let's Explore

Would the eggshells support more or less weight if the small end of the shell was used? Repeat the experiment, but break off the large end of the shell. Record the number and weight of books that caused the first crack and then the number and weight needed to crush the shells. Science Fair Hint: As part of a project display, prepare new shells from the large (rounded) and small (pointed) ends of the eggs. Exhibit the shells supporting lightweight books. Label the display with the total amount of weight that each set of eggs can support.

### Show Time!

1. How are molecules arranged in solids? Molecules in solids are not packed tightly together; much space exists in a solid. Explain and diagram how the "holding forces" among the molecules in a solid give it a definite shape and a definite volume and affect its strength.
2. Observe and collect samples of different types of solids. Make comparisons and draw conclusions about the strength of each type of material. Make a list of questions such as these about the samples collected and discover the answers: Are all wooden pieces hard? Can all samples of cloth be easily torn, and does the cloth tear with the same ease in all directions? Do all paper samples have the same strength? Display the samples, a list of your questions, and the answers to each question.

### Check it Out!

Weight can be successfully hung from some solids but not from others. This is due to the tensile strength of the material. What is tensile strength? Which solids have great tensile strength?