Dropping Eggs

19 July 2009

Part of the show Making Babies - Pregnancy and Fertility

egg.jpg

Credit:

Dave Ansell

Ingredients

	Lemonade Bottle		Scissors
	Salt		Eggs
	Tape

Instructions

First try protecting the egg using just a strong box.

Cut the bottle open around the widest part.

Put an egg in the bottle and tape the bottle back up.

Try dropping it from about waist height.

Now try filling the bottle with salty water. Keep adding salt until the egg starts to float.

Try dropping the bottle from waist height. Do you get the same result?

Result

The egg just in the bottle will smash, but in the salty water it should mostly survive.

Explanation

If you drop an egg on the floor its speed changes from about 3m/s to stopped in a very short period of time, this means that is accelerates (decelerates) very rapidly. A large acceleration requires a large force and because this force is concentrated in one place the eggshell isn't strong enough to support this force and it breaks.

Egg afterwards

When the egg hits the floor it is slowed by a large force from the floor.

This large force causes the shell to break.

If you put the egg in a bottle the egg still stops rapidly and the force is still concentrated in one place so the egg still breaks.

Egg broken in a bottle

In a bottle the egg is still stopped very rapidly by a large force in one place.

Again this breaks the egg

However if the egg is floating in a fluid then the force that slows down the egg is upthrust, the same force which was making it float in the first place, which gets larger the larger the acceleration of the bottle.


The egg is accelerated by the upthrust from the liquid which is an evenly distributed force.	The egg is good at resisting this type of force and survives.

This is one of the reasons that an unborn baby is surrounded by salty amniotic fluid because the baby is a similar density to the amniotic fluid it is floating, so if there are any impacts to the mother the forces are evenly transferred to the baby not doing it any damage.