Today, as part of the summer science and math camp, they had a guy from Boulder Blasters come and teach the kids how he breaks boulders. He also taught the the difference between compressive and tensile strengths of rocks. Since a rock is ten times stronger in compression it is much easier to break the rock with tension. Rather than use a large machine to pull the rock apart, they use a small explosive to break the rock from the inside out. To do this he used a pneumatic jackhammer-like drill to create a hole deep into the rock. Then he filled the hole to the top with water and inserted a small explosive, very similar to a shotgun shell. Then, attached to a string, a firing pin on a steel block was set on top of the hole. When he pulled the string the firing pin plunged into the water, setting off the built-in firing pin in the explosive. When this explosive went off it split the rock into three pieces from the inside out. It was a very impressive and entertaining demonstration.
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