Explore integer multiplication by considering the trajectory of a hot air balloon as it rises and falls in this interactive from MPT. In the accompanying classroom activity, students play a game in which they find the product of two integers and move a button the corresponding distance and direction along a number line. Next, they use the interactive. To get the most from the lesson, students should be comfortable using a number line to add positive and negative integers, and they should be familiar with the notion that numerical opposites sum to 0. For a longer self-paced student tutorial using this media, see "Multiplying a Positive Integer with a Negative Integer"on Thinkport from Maryland Public Television.