Teaching about Inertia

Spinning eggs

If you are anything like me, you have probably prepared hard boiled eggs once, wanting to eat them the next day and put them back into the fridge. And when you’ve wanted to take them out the next day, you realized you put them right next to the raw eggs. What now? I admit, this happens more often than I would like it to be true. What a relief that I can use physics to help me find my hardboiled eggs.

I really don’t want to eat a raw egg. But which one is the hardboiled egg and which one is raw?

How do I distinguish between the eggs?

The two eggs differ only on the inside and this is what we have to keep in mind. The hardboiled egg has – as the name suggests – a hardened inside. Whereas the raw egg is fluid inside.

How does this experiment work?

On the inside of the hardboiled egg, everything moves together and will continue to do so. It is one solid mass. Mass is a measure of inertia, which is the measure of how difficult it is to move a stationary object. When rotating, the egg has rotational inertia.

The raw egg has a solid shell but the egg yolk and egg white inside can move independently of the shell. Each fluid has a different inertia, which is why they rotate at different speeds. Thus the rotation of a raw egg is more of a wobble than a spin. Ultimately, the raw egg will stop spinning.

Do you want to do the experiment yourself?

Items Needed

  • One Raw Egg
  • One Hard Boiled Egg


  1. Prepare a bowl of one raw egg and one hardboiled egg.
  2. Take one egg out of the bowl and spin it on the table.
    Helpful Tip: It is important to spin the egg on a hard flat surface.
  3. Next, repeat with the other egg. Observe the behavior each time you spin an egg. One of the eggs behaved differently than the other two. This is the hard boiled egg.

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