Wednesday, April 1, 2015

How Strong is an Egg?

With Easter fast approaching we have been preparing lots of eggs - from dying them to making geodes.  We are discovering that these are pretty fascinating structures and made for some great structural exploration and a fun set of Easter science activities.  In particular the eggs shape proved to be a pretty important factor in its strength.

Egg Shape Experiment 1:  Can You Walk on Eggs?


We started by looking at the shape of an egg and talking about how it is almost oval in shape.  Then I asked the girls if they thought they could stand on an egg.  They both immediately said no.   So I suggested we test that idea and setup our experiment {we did the experiment outside and I put garbage bags down to catch any broken eggs as I was not sure how this would go!}.


The girls were very nervous at first and carefully placed a foot on the eggs without any weight.  None of the eggs broke!


They started to get more confidents so I asked if they could walk across them like a balance beam!




To their surprise they were able to walk across them!  None of the eggs broke.  But do notice the careful foot placement of my 4 year old.  She has her feet in the middle of the eggs so she has about 5+ eggs under each foot.  Her weight was definitely distributed.   When my 2 year old walked on the eggs the eggs did break.  Most of the time this happened when she had her heel on one egg and her toes on a second egg.  Her feet were so small that it was hard to distribute her weight across enough eggs.


After a few times of walking across the eggs the eggs did begin to break with either girls walking on them so there is a definite limit on the number of times you can walk across.  This all lead to a great discussion why the eggs broke and in particular why our bigger child was able to walk on the eggs and our smaller (and lighter) child was not.  The girls learned a lot from this!

Egg Shape Experiment 2:  How Strong is the Shape of the Egg?


So we wanted to know just how important the egg shape is for the strength of the egg.   We noticed that all the eggs in the containers were pointing up (and apparently hens sit on them this way as well).  To test this we cut a hole in one end of four eggs.  We then cleaned the eggs out and finally cut the eggs in half so that we had an arch standing on the table.  We placed the four egg shells on a cookie sheet and took it all outside to test how many pieces of wood they could hold.


This looked like a pretty interesting setup and even attracted some of the neighbors to watch and help!  We started by placing a plastic container on top of the egg shells.  The girls were pretty impressed that the egg shells did not break.  


The kids all took turns then adding logs to the bucket.  We had to be a little careful as the logs could cause the container to fall over if they were put to one side.  Next time I would use a flat surface to place the logs on.  


The eggs still held up when we added the logs to the bucket.  We kept on going, adding a few more logs.  The kids put the logs to one side and one of the egg shells broke so we removed the broken egg and placed the bucket on the three eggs and kept on adding logs.   {Be very careful when putting the logs on the eggs as the eggs will crack if they move.}


We kept on going and even had to get some more logs (they were pretty dry and light) until one big log was added to our pile and crunch - all the eggs collapsed.




In total we were able to put six logs on top of our bucket before the eggs broke.  It showed just how strong egg shells really are.  After all they have to be strong enough to be under a chicken.  So why is the shape so strong?  Well the shape of the egg is an arch or dome shape - it does not have any corners.   Therefore there are no points on the surface of the egg that will get focused weight applied from the top.  The arch or dome shape evenly distributes a force applied to the top over the whole structure.  This makes it one of natures strongest shapes!


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Supplies:
Exp 1:

  • Two dozen eggs
  • Garbage bags

Exp 2:

  • 4 Eggs
  • Kitchen shears
  • Cookie sheet
  • Bucket/flat wood sheet
  • Logs


Instructions:
Exp 1:

  1. Place two dozen eggs in their container on top of garbage bags.
  2. Encourage your child to walk across the eggs 

Recommended for ages 3 and up.

Exp 2:

  1. Take 4 eggs and make a hole at the bottom of the egg to empty the egg.
  2. Cut the egg in half so that you have an arch (big or little endian).
  3. Clean the egg shells gently and place open side down on a cookie sheet.
  4. Place a bucket/flat wood sheet on the egg shells.
  5. Carefully keep on adding logs to the bucket until the eggs break.  


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