Hundreds of Iowa high schoolers are taking part in the 25th annual Physics Olympics today at Drake University in Des Moines. Doctor Jack Gerlovich, a Drake professor of science education, says the various events and challenges are designed to stimulate the young minds by making them use ordinary household items for extraordinary feats. Students have to create a self-propelled catapult that will travel two meters along a specific course, using only a mousetrap for its power, to launch a ping-pong ball at a target five meters out.Other challenges include building a strong scale-model bridge out of toothpicks and making a human-powered water heater, where teams have five minutes to raise the temperature of a vat of water using only human power. Gerlovich says another event is called the Soda Straw Arm. They have to build an arm out of 20 straws to hold a 50 gram weight.The competition is underway from 8:30 AM to 12:30 PM.