Experiment with inertia and momentum: The spinning egg

Description:

Learn about inertia and Newton’s First Law of Motion.

Equipment needed:

One raw egg (or more, if you’re clumsy!)

One hard-boiled egg

The Digital Bits Science Lab Experiment:

This experiment is often described as “how to tell a raw egg from a hard-boiled egg without breaking them”. You simply spin both eggs on a flat surface: The egg that spins smoothly is the hard-boiled egg. The egg that wobbles as it spins is the raw egg.

What’s happening here? The hard-boiled egg spins smoothly and quickly because the egg inside is solid. The raw egg wobbles as it spins because the egg inside is liquid. As the egg is spinning, the liquid inside sloshes around, and affects the egg’s spin. Why does this affect the egg’s spin? It’s because of Newton’s First Law of Motion. This law states: “An object in motion remains in motion, unless acted upon by an external force.” Put more simply, Newton’s First Law says, “if something is moving, it’ll keep moving unless something else stops it”.

Here we have our example of Newton’s First Law of Motion, the raw egg. Try this: give the raw egg a good spin. As it spins, stop the egg by quickly putting your finger on the top of the egg. Then just as quickly, remove your finger. This action should be fast, perhaps half a second at most. When you remove your finger, you’ll see the stopped egg begin spinning again!

The egg keeps spinning after we stop it because the liquid egg inside remains in motion. The shell of the egg was stopped by our finger, but the inside keeps on going.

Within seconds, the raw egg will stop spinning. This is because of many factors: The friction between the table and egg will slow the egg and eventually stop it. Though the liquid inside the egg keeps moving, it too slows down and stops because the hard shell contains the liquid and eventually prevents it from moving.

Other articles related to this topic:

• Learn about a compass and earth’s magnetic poles
• Power a boat with surface tension: Make a “zoomer”
• Learn about air pressure with a piece of paper
• Heat is energy
• Levitate your arm with muscle memory