Each group needs:

• 3 worksheets, one each per student
• 1 spring scale, for measuring applied forces
• plastic sandwich-sized bags
• 8-12 rocks, about 2 inches (5 cm) in diameter
• flat piece of wood, ~2 ft long X 1 ft wide X 1 inch thick (60 cm x 30 cm x 2.5 cm)
• stack of textbooks, ~1-1½ feet high (30-45 cm)