All Resources

Egg Spinning

In this demonstration, students discover a practical way of determining whether or not an egg is raw or hard-boiled using Newton's First Law of Motion regarding an egg's centre of gravity.

Inside its shell, a hard-boiled egg is solid whereas a raw egg is fluid.

  • When you spin the raw egg, its centre of gravity (or balance point) changes as the fluid inside the egg moves around. This results in a wobbling motion in order to achieve balance.
  • When the hardboiled egg is spun, the solid centre has a fixed centre of gravity, causing it to move at the same time as the shell. This results in a smooth, balanced spin.

Trying to stop the egg from spinning is an excellent application of the principle of momentum. The raw egg keeps spinning after you touch it briefly because the liquid egg inside remains in motion, it's inertia is greater than that of the solid interior of the hardboiled egg. An object's momentum is its resistance to changing its state of motion; roughly "how hard it is to stop".

This is related to Newton's First Law of Motion: "An object in motion remains in motion, unless acted upon by an external force." Put more simply: if something is moving, it'll keep moving unless a force stops it. The friction between the table and egg will slow the egg and eventually stop the spinning. Though the liquid inside the egg keeps moving, it too slows down and stops because of the friction between the hard shell and the table.

Objectives

  • Illustrate a practical application of Newton’s First Law of Motion.

  • Describe the principle of inertia.

  • Describe how an unstable centre of gravity affects balance.

Materials

  • Per Demo or Group:
    1 raw egg
    1 hard-boiled egg
    a table

Key Questions

  • How can you tell which one is raw and which one is hard-boiled?
  • What is happening inside the raw egg when it spins?
  • What is happening inside the hard-boiled egg when it spins?
  • Which one do you think will spin more smoothly?
  • Why does the cooked egg spin better than the raw egg?
  • Why does the raw egg keep spinning a bit after stopping it? Why doesn’t the cooked egg do the same thing?

What To Do

Preparation

  1. Hard boil 1 egg and let it cool so that it is the same temperature as the raw egg.

Demo

  1. Show the class both eggs.
  2. Tell them that one is hard-boiled but you have forgotten which one. Invite suggestions as to how to tell the two apart.
  3. Set both eggs spinning on the table. The hard-boiled egg spins well whereas the raw egg wobbles.
  4. Set the eggs spinning again.
  5. As soon as the raw egg starts spinning, touch it briefly with your finger just long enough to stop it. When you take your finger away, the egg will continue to spin for just a quick second. Try the same thing with the hard-boiled egg, unlike the raw, it will just stop.

Extensions

  • How will a soft-boiled egg spin?
  • Experiment with spinning plastic eggs (available near Easter time) filled with different solids or liquids.
  • Check out how this relates to our sense of balance when we spin

Other Resources

Science World | YouTube| Inertia