The Floating Egg Experiment

This past weekend my 5 year old daughter and I did a very cool science experiment called the "Floating Egg".  As you can guess from the title, the goal is to make an egg float, but not just make an egg float on top of a glass of water, but make the egg float in the middle of the glass of water.  The science behind this revolves around density.  If the egg is more dense than the water, the egg sinks.  If the egg is less dense than the water, the egg floats to the top.  But how do you get the egg to float in the middle?  That's trickier.  To start we filled a water bottle half full of regular tap water.  Then we dropped the egg in.  Here's the video of our drop.

As you can see, the egg sank to the bottom because the egg density is greater than the water density.   Next we filled a second water bottle half full of water, but then put several tablespoons of salt in the water.  The salt increases the density of the water.  If the density exceeds that of the egg, the egg will float.  Here's our video of the egg in salt water.

Our first attempt failed because we didn't add enough salt, so with the egg in the water, we added salt until the egg started to float.  Now the tricky part is figuring out how to make the egg sink, but only halfway to the bottom.  To do this, take a glass of tap water and slowly pour it into the salt water mixture.  By pouring slow, the tap water won't mix with the salt water.  It's very similar to oil sitting on top of water except you can't see a clear division between the tap water and the salt water.  When the egg is dropped into this 2 fluid mixture, the egg sinks through the tap water, but floats on top of the salt water layer.  Thus it looks like the egg is magically floating in the middle.  

Although this isn't a complicated experiment, it looks cool seeing an egg float in the middle of a water bottle filled with water.  We let the bottle sit for awhile, and several hours later, the egg was still floating.  Very cool!  Grab your kids and give it a try.

Update:  We checked again in the morning and the egg was still floating in the middle!