Lesson 4
Home Up Lesson 1 Lesson 2 Lesson 3 Lesson 4


Mr. Fizzix Physics


Joanne Pirog


Lesson Plan IV


Volume and weight of a balloon filled with water. The Trebuchet project involved the launching of water filled balloons that weighed sixteen pounds. We used *in class 9‑inch balloons. This 9 'inches was the diameter of the balloon. We filled it with water to its full capacity (volume). We wanted to figure out how heavy this balloon would be by using its volume formula. The formula we used was V = 4/3 pi r^3 Example: 9‑inch balloon, diameter = 9 in. The radius is = 4.5 in. We used


3.14 for pi.


V  =  4/3 (3.14) (4.5)^3

V  =  381.4 cu in

Change to centimeters using (2.54 cm = 1 in)

V  =  (381.4) (2.54cm/in)^3

V =  (381.4) (16.4) = 6250 cm^3 = 6250 grams

and 6250/454 ~ l3.5pounds


Next have students actually fill up the balloon and actually weigh them to see if our mathematical expectations actually materialize.


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Last updated: November 13, 2002.