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why do some things float and some sink

After spending 342 consecutive days onboard the International Space Station from 2015 to 2016, astronaut Scott Kelly now holds the
for longest single space mission by an American. But his "One-Year" study with NASA was about more than breaking records: Its purpose was to show how prolonged time in orbit would effect Kelly's genetic makeup compared to that of his identical twin brother on Earth. Now, following recent evaluations of the two men, it appears that Scott Kelly and his brother Mark are no longer genetically identical, reports. NASA the most recent findings from its ahead of a more comprehensive paper combining the work of multiple teams of researchers that is slated for later in 2018. Like his brother Scott, Mark is also an astronaut, making the pair the only twin astronauts in history. So when NASA was looking for a way to study the long-term effects of space life, the siblings were a perfect fit. As Scott was sending and on the ISS, Mark stayed on Earth to serve as the control. Biological samples taken from both subjects before, during, and after the space flight showed some dramatic differences.

According to an investigation conducted by Susan Bailey of Colorado State University, Scott's telomeres, the protective "cap" at the ends of chromosomes that shorten as we age, got longer in space. The telomeres began shrinking back to preflight levels, however, a few days after Scott's return to Earth. Scott was subjected to regular exercise and a restricted diet aboard the ISS, so the new lifestyle may explain the sudden telomere boost. Other genetic differences stuck around even months after landing. "Although 93 percent of genes expression returned to normal post-flight, a subset of several hundred 'space genes' were still disrupted after return to Earth," acccording to a NASA. About 7 percent of Scott's genes may show longer-term changes, included the genes associated with DNA repair, immune health, bone formation, hypoxia (an oxygen deficiency in the tissues) and hypercapnia (excessive carbon dioxide in the bloodstream). A long list of factors, like radiation, caloric restriction, and zero gravity, may have contributed to the results. NASA plans to use these findings to develop countermeasures against these effects, which will be essential if the agency plans to send humans to Mars, a journey that could take three times as long as Scott Kelly's ISS mission. [h/t ] Students are given a plastic tub filled with a variety of materialsвwood of different sizes and shapes, a pencil, a marble, a styrofoam ball, a cork, a plastic spoon, a rubber band, a penny, a toothpick, a paper clip, and whatever else is handy.

They are asked to predict which objects will float and which will sink when placed under the level of the water and let go. Students perform the experiment and compare the results to their predictions. They discuss why they thought certain objects would sink/float. The class brainstorms a list of properties of the different objects that may affect whether the object floats or sinks. Using the objects they already have, students do simple tests to rule out some of the properties (such as color, shape, etc). In the end, it should be apparent that the most important properties are mass and volume (the instructor needs to guide the class to this conclusion). The students are then given a second set of materials, five film canisters and at least 50 pennies, with which to test the effect of changing the mass and volume of an object (or system, in this case) on whether the object floats or not (See Activity 2 handout).

Students are asked to design and perform an experiment that only changes one of these properties (mass or volume) while keeping the other constant and then seeing how a change in the property affects whether the object sinks or floats. Before running their experiment, they make a prediction and record why they think their prediction is correct. They run their experiment, take data, and record their observations. They then compare their results to their prediction. Next, they go back and design a second experiment to test the other property (mass or volume), record predictions, run the experiment, make observations, and then compare their results to their prediction. After they have completed both experiments, they do a Check your Understanding question and predict how many film canisters they would need to use to float 50 pennies. After making a prediction, they test it by performing the experiment.

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