Tuesday, 19 April 2011

Egg Crash Test Stats

As part of a Sixty Symbols Easter series, we've performed a series of "crash tests" on Cadbury Creme eggs.

They were performed at the University of Nottingham's Biomechanics Lab.



Dr Donal McNally, who oversaw our light-hearted "eggsperiments", has subsequently sent me the following facts and figures. The stuff at the end about calories is amazing!

DONAL SAYS:

"Here is the load deformation graph for the creme egg compression test you filmed. The egg deformed about 5.8mm (12%) before it started to fail. Once a crack had started, the load required to continue the failure dropped until the egg had compressed to about half its original height. After that, the force required to displace the gunge sideways to allow continued compression started to go up. The energy to initial failure was about 0.3J compared to 712,000J of chemical energy (170 Calories) it contains.


Click for bigger version of graph

DONAL CONTINUES:

"At higher speeds (such as the Charpy tester) there is less time for the viscous centre to move out of the way so it has to move faster and therefore the viscous losses are much greater. In our case it turned out to be 11-14J compared to the 1.8J in the compression test for a similar level of disruption.

"The drop tower was simply overkill. The energy I wrote down on the bit of paper (150J) was the kinetic energy of the impacting weight. This is much greater than 14J. Interestingly the weight of the weight (as it were) is about the same as the quasi-static failure load in the original compression test.

"The kinetic energy of a 39g egg at 11ms-1 is 2.4J (the crash track test). The impact contact time is very short and the energy considerably smaller that that observed in the Charpy test. This is why the egg was hardly damaged.

"The difference between chemical energy density and mechanical energy density is huge. A creme egg would have to be moving at more than 6000ms-1 (Mach 20) for its kinetic energy to match its chemical energy. This is why petrol (and creme eggs) make excellent fuel. Similarly, your Mini car would need to do 77mph to have the same kinetic energy as the chemical energy in a creme egg."


By the way, here's what we did to some Creme Eggs last year in the name of chemistry!!!

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