"Will it Float or Sink?" Mystery Bag Density

This comprehensive and engaging hands-on activity is the perfect gateway for introducing students to the concept of density using the intuitive phenomenon of floating and sinking1.Students will move beyond the misconception that “heavy things sink” 222by investigating various common objects in water, transitioning from simple prediction and observation to actual measurement and calculation3.Key Features & Learning Outcomes:Hands-On Activity: Includes a step-by-step procedure for a “Mystery Bag Challenge” 4444, where students predict (no peeking!) and then test whether 10-12 common objects float or sink5.Data Collection & Calculation: Guides students (Grades 3-5/6-8) through measuring mass and volume (using water displacement) for several objects, then calculating density ($D=m/V$)6666.Core Concepts Explained: Clearly defines density as “mass $\div$ volume” 7and establishes the floating condition: objects with density less than $1~g/cm^{3}$ float, and those greater than $1~g/cm^{3}$ sink8.Discussion Prompts: Features high-level follow-up questions to debunk common myths, such as why a huge steel ship floats while a small steel nail sinks (due to air space lowering overall density)9.Adaptations & Extensions: Includes age-specific adaptations (K-2 to 6-8) 10, connections to real-world examples (submarines, fish swim bladders) 11, and advanced extensions like creating a liquid density column or a Cartesian diver demo12121212.Teacher Reference: Provides scientific background, common misconceptions/corrections (e.g., Apple floats at $0.88~g/cm^{3}$ while Grape sinks at $1.25~g/cm^{3}$) 131313131313131313, and NGSS alignment14.This high-engagement activity consistently introduces density across elementary and middle-school curricula worldwide15.