To build our lab we cut about 2.5 meters of string. We then strung the string through the pen tube, on the end of the string coming from the top of to tube we tied a rubber stopper. On the other side we tied a water bottle. Then we mark 3 different lengths to the top of the string, 1 meter, .75 meter, and .5 meter. These markings were later used so we could tell if our radius was consistent. After we build it we practiced spinning it using different amount of water to see what length worked best for each amount of water. We determined that for more than 400 grams of water a radius of .75 meter works best and anything under that .5 meters works best. Heavier weights require a longer radius to stay aloft.
Step 2 - Trials
To collect data we ran 11 trials, 6 trials between 100g and 400g using the .5 meter radius, and 5 trials between 400g and 700g using the .75 meter radius. In each trial we measured how long it took for the stopper the travel 30 revolution at a set radius, and compared that to the weight of the water and the water bottle. Each trial had a different amount of water in the water bottle. With the data we collected we created a graph, weight being the independent variable. The heavier the object/water, the faster the stopper spins because more centripetal force is needed to hold up the object. We then created a line of regression using the graph. With the line of regression we can find the weight of an object by timing 30 revolutions.
Step 3 - Tests
Once we created a line of regression for both of the data sets we ran several tests. The first test we ran was in the lower weight bracket. We filled the water bottle with an unknown about of water and did not weight it. We had to guess that it would fit within the lower bracket. We then timed how long it would take for the stopper to travel 30 revolutions. It took 10.93 seconds, we then plugged that into the line of regression, and came out with a weight of 262.85 grams, the real weight was 216 grams. We also ran 2 test in the heavier weight bracket, which were both accurate.