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Eggstra Strong Eggs

Even though eggshells are fragile, the dome shape of the shells provides strength. In this demonstration students will marvel at the amount of weight four eggs can carry. 

Arches and domes are used in many forms of architecture including roofs, bridges, and igloos. The arches in the dome shape distributes the weight and pressure applied on the top evenly throughout the entire structure.

Although eggs are easily cracked if hit on the side, the dome-shaped ends will support a great deal of weight. This is due to the fact that weight pushing down on top of the dome-shaped egg does not push straight down: the weight spreads outward along the curve of the egg. 

Objectives

  • Relate the strength of an egg to its structure.

Materials

  • Per Class or Group:
    4 raw eggs (or hard boiled for less mess)
    4 pop bottle caps
    a piece of poster board 30 cm x 30 cm (12 in x 12 in)
    a vinyl/plastic tablecloth
    lots of large and heavy books (like dictionaries or textbooks)
    weighing scale (optional)

Key Questions

  • How many books will the eggs be able to hold?
  • Would the eggs support more or less books if they were balanced on their sides?
  • Why are arches and domes so strong?

What To Do

  1. Cover the table with a plastic tablecloth.
  2. Place the eggs in the four bottle tops, narrow end down.
  3. Place the four bottle tops in a rectangle, about 20 cm x 15 cm (8 in by 6 in).
  4. Put the piece of poster board over the eggs.
  5. Begin placing books on top of the poster board.
  6. Record how many books (or how much weight) the eggs hold before they break.

Extensions

  • Try the same experiment with the eggs balanced on their sides.
  • Use empty eggshells. This is a good option if the experiment is an activity rather than a demonstration:
    1. Use the edge of a spoon to 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 a bowl, then rinse the inside of the eggshells with water. Carefully dry the outside of the shells with a paper towel.
    3. In order to have the eggs the same height and even on the bottom edges, wrap a piece of masking tape around each egg. The position of the tape should be the same on each shell.
    4. Use scissors (fingernail scissors work best) to cut away the broken ends of the shell from around the bottom of the tape on each shell.
    5. Place a book on top of the shells, and position the shells so that one is under each corner of the book.
    6. Carefully add books, one at a time to the book on top of the eggshells, waiting a few seconds before adding the next book.
    7. Stop adding books when you hear a cracking sound. You can use a bathroom scale to determine the weight of the books supported by the eggshells.