Motivating Students With Discrepant Events

One of my favorite discrepant events from the Princess Bride.  Of course the explanation is that the Dread Pirate Roberts put the poison in both glasses! Many science teachers use discrepant events to get students excited about science.  Last week I used a discrepant event in class and it went over very well.  Basically, I took a balloon and blew it up and lit it with a lighter.  It popped very loudly and my 7th graders loved it.  Then, I took another balloon filled with water and blew it up.  I suspended it over a student's head (another fun thing to do) and asked that they predict what would happen if I lit it with the lighter.  Most thought it would again explode and water would splash down on the unfortunate student.  One student even put her hood on. This event works because the specific heat of water prevents the balloon from  bursting.  It does leave a great black spot on the balloon, however.  I like to be very dramatic during these demonstrations which gets everyone in the mood for science!  Discrepant events work well because students will want to know why that event turned out the way it did.  I like to use the P.O.E. method while I demonstrate.  P = predict what is going to happen, O= observe what does happen, E = explain why it happened the way it did.