Elegant Eggs

The shape of eggs gives them surprising strength.

Have you ever made a scrambled egg or an omelet? Is it hard to crack an egg? No, not at all. You know, egg shells are made of the same material as a stick of chalk. This very brittle material breaks with just a small amount of pressure. Let’s see just how weak or strong eggs really are.

1. Ask pupils to remove any rings from their fingers of one hand.
2. Place a raw egg in the palm of a pupils hand and hold their hand over a sink or a garbage can.
3. Instruct pupils to close their fingers over the egg and squeeze it as hard as they can.
4. Repeat this process with as many pupils as would like to try it (replace the egg after every few students, just in case of hairline fractures).
5. What happened? Why do you think this is?

Why couldn’t you break the egg? It’s not hard to break an egg against the edge of a frying pan, and it’s not hard to break a piece of chalk, which is made of the same material as egg shell. What’s different about trying to break an egg by squeezing?

Simple explanation

Unlike the edge of a frying pan, your hand doesn’t have any sharp edges (that’s why we removed any rings on our fingers). Also, the egg has a curved shape. This helps spread out the pressure from squeezing. By spreading out the pressure, no single spot on the egg gets too much force.

More complicated explanation

The curved shape of the egg transfers the force of your squeezing hand across the entire surface of the egg. So no single spot on the egg has to resist all that pressure. Also, because the egg is roundish, as the pressure travels around the egg, there is always more egg shell in front of the spreading pressure to resist the force.

Eggshells are made up of tiny crystals that are arranged in a special pattern that gives them strength. It's like when you build a tower out of blocks, if you put the blocks in a certain way the tower will be strong and won't fall over easily.

Often, to make something stronger, we add more material to it. It’s easy to break one piece of dry spaghetti, for example, but harder to break a handful of dry spaghetti. Egg shells are very thin and yet also very strong, not because of lots of material, but because of shape.

People who make things have learned from nature, such as the curved shape of eggs, to make things stronger without having to add more material. Strengthening curves can be found from the utensils in your kitchen to bridges and buildings. Can you find a local example?

Using less material to make things is good for our environment, because it requires less mining and less energy use, and results in less waste. Using less material also saves companies money, making products less expensive to buy.

Some STEAM opportunities include:

• Identify and compare suitability of everyday materials.
• Find out how shapes of solid objects can be affected by shape.
• Consider how the properties and shape of different materials makes them suitable for different tasks.
• Think about unusual and creative uses for everyday materials.
• Comparing the properties of different materials.
• Asking questions and making observations.
• Carrying out simple tests.
• Making predictions.
• Using scientific evidence to answer a question.
• Apply learning to real world problems.