This Flash animation lets students interactively explore how density is related to weight and volume. A cylinder filled with water rests on a scale. Use the mouse to “”drop”” a wood block, a rock, a canned food item, or a half-full jar of pickles into the water, then view the displacement and calculate the density. If the object floats, use the mouse to push it under the water to complete the calculation. A weight density calculator is provided alongside the animation for additional support. This material is part of GROW, an NSF-sponsored collection of resource materials for civil engineering, supporting K-20 education. The developers have focused on interactive, multimedia educational resources that are “”story-booked”” to emphasize active learning.