Egg-straordinary physics tricks

You will need:

raw egg
hard boiled egg

What to do:

Place the two eggs on a flat surface and set them both spinning.
Gently and briefly place your finger on the top centre of each egg.
Notice that the hard boiled egg is much easier to spin, but it stays still when you take your finger off. In contrast, the raw egg is difficult to start spinning but will keep spinning when you take your finger off.

What’s happening?

Momentum is the key to this demonstration. A raw egg is filled with a liquid, whereas a hard boiled egg is effectively a solid. Firstly consider what happens when you stop the eggs: When you gently place your finger on the top, you stop the outer shell of both eggs from moving. Since the hard boiled egg is solid, all of the egg stops moving, and so the egg remains stationary when you remove your finger. However, the liquid inside the raw egg will keep spinning even though the outside shell is stationary. The drag of that liquid on the shell will start the raw egg spinning again. Similarly, a hard boiled egg is easier to spin since the entire egg starts spinning at the same time, whereas in the soft boiled egg only the outer shell is spinning at first, and gradually the liquid insides begin to spin as they are dragged around by the shell.

Tips for Success

Don’t set your eggs spinning too hard or they may roll off the table. Make sure you start them spinning at approximately the same rates or your audience may think you are trying to fool them! As if!

Another egg-sample of physics at work:

Eggs are traditionally thought of as being very fragile, but in fact the physics behind their shape is astounding.

You will need:

raw egg
plastic bag or glove (for the unconfident!)

What to do:

Challenge audience members to break the egg just by squeezing it. Let them wrap the egg in a plastic bag or wear a glove if they're worried… Believe it or not, it can't be done! Shift it Mr Doppler!

What’s happening?

The shape of an egg is actually one of the strongest designs possible. The curved structure means that applying pressure to any particular area actually spreads the force out over the entire egg. So just squeezing it won't cause it to break. Of course applying a very sharp force to one point WILL cause it to break – which is why we usually tap the egg on the side of a bowl to break it when cooking.

Tips for Success

Ask your volunteers to remove any rings etc. before trying this trick – the sharp uneven force from such metal objects can cause the egg to break.

Check your eggs for hairline fractures before attempting this trick – if there is any existing damage to the egg it won't work.

Did You Know?

The ornate and intricate arched doorways and ceilings in many old buildings aren’t just there for their aesthetic qualities. Arches are in fact one of the strongest building structures. In effect, every brick or piece of masonry within the arch is falling on all the others, distributing the weight evenly over the structure.