Go Suck an Egg!

Introduction

Have you ever been helping in the kitchen and found yourself with a recipe that calls for egg whites? Do you use the egg shell to separate the egg yolk from the egg white? Instead of using the shell to separate them, you can use science! In this activity, you will use simple tools to explore how physics can help you do everyday tasks – such as separate egg yolks from egg whites.

Background

Although they’re invisible to us, our world is full of air molecules, filling the air all around us. Even though you can’t see them, you can feel them moving if you fan your face with your hand. That gentle puff of air on your cheek is caused by air molecules!

Although we can’t see them, air molecules still exert a pressure or force on everything in our world- including you! You can feel the pressure of those air molecules by filling your cheeks with air.  Press against your cheeks – notice how firm they feel. Can you push gently against your cheeks and move the air from side to side in your mouth?

It’s just air inside your mouth, but those air molecules exert a force against the sides of your cheeks. The force of air molecules is important in this activity. Those air molecules will act on the air inside a bottle, giving it some pretty amazing kitchen super powers!

Materials

Preparation

Procedure

Observations and Results

In this activity, you used a plastic bottle to separate and move an egg yolk from one plate to another. How cool! However, when you used a bottle that had a hole in the bottom, you likely found it impossible to suck up the egg yolk. When you covered the hole with your finger, you could move the egg yolk again.

Why did adding a tiny hole in the bottle ruin it’s amazing ‘egg vacuum’ powers? The simple answer is – vacuums don’t work if they have holes in them! To understand this, we need to understand why the bottle was able to suck up the egg yolk in the first place.

You were able to use you your water bottle to pick up the egg yolk because of air pressure. Even though it looked empty, your water bottle was full of air. When you squeezed the bottle, you pushed out some of that air. Putting the bottle on top of the egg yolk created a seal on the bottom – just like a lid. No more air could come in or out of the bottle. When you released the sides of the bottle, you created more space inside of it, but no more air could get in. Because there was less air inside the bottle, but more space, the inside of the bottle had lower pressure than the outside. The higher air pressure on the outside pushed the yolk inside the bottle!

However, when you cut a hole in the bottle, you made it possible for air to move in and out of the bottle, even when the yolk was sealing the bottle top. As a result, when you released the sides of the bottle, more air rushed in through the hole to fill that space. Therefore, the air pressure inside the bottle was always the same as the air pressure outside the bottle, and there was no force to push the yolk. When you covered the hole again, you sealed the bottle, so it behaved as though there was no hole.

More to Explore

• Fallen Arches: The Surprising Strength of Eggshells, by Science Buddies
• Egg-cellently Cooked Eggs: The Process of Soft-Boiling an Egg, by Science Buddies
• Science Activities for All Ages!, from Science Buddies

Credits