Density & Buoyancy - What causes something to sink or float?

(1) Look at the objects you have been given and predict if you think they will sink, float or remain suspended (neutral buoyancy). Record your predictions. After everyone has submitted their predictions, compare the class predictions and identify those objects whose behavior was most difficult to predict. (See summary data)

(2) Form combinations of blocks (see photos) by tying them together with rubber bands such that the total mass of each combination is less than 120g. Find one combination that will float and one combination that will sink for each of 1-block, 2-block, 3-block, 4-block and 5-block combinations. Determine the masses of each combination and record in the appropriate column of the data table. You may mix blocks from the various sets and use more than one of each material when making combinations.

After analyzing your data and the class data, please answer the following questions. Enter your answers in the quickwrite.

  1. Under what conditions will an these cube formations float in water?
  2. Under what conditions will they sink?
  3. What determines if an object will sink or float?
  4. Why does a steel ship float?

(3) Measure the mass and volume of a diet and regular soda. Based upon your measurements, do you think diet will float or sink? How about regular soda? Enter your prdictions in the QuickWrite. Were your predictions correct? If not, why do you think so?

  • Examine the Obesity trends in the US and describe all trends that you notice, and record in the QuickWrite. in the column specified by the instructor.
  • What hypotheses do you have regarding obesity trends and soft drink consumption. QuickWrite.


4) Based upon what you have learned so far, what do you predict will happen if salt water is placed upon fresh water, and what will happen with fresh water is placed upon salt water? Summarize the predictions in the QuickWrite. in the column specified by the instructor.

  • Observe the instructor demonstration and explain the following activities:
    • fresh /salt water
    • salt / fresh water
    • cold / warm water
    • warm / cold water
    • candle & CO2

Applications to everyday life