The theme of this week ended up being air and gas pressure. We started out with an experiment. In this experiments, withing our new lab groups, we designated on of the five people to sit on top of a trash bag. This bag had four straws attached. Our mission was to work together to blow enough air into the bag to lift the person off of the ground. Our group managed quite well despite some of us becoming lightheaded.
Next, we watched a demonstration by our teacher about how temperature affected air pressure. A soda can, after being heated, was placed upside own into colder water, which captured the hot air within, and caused the can to quickly contract. This, we found out, was because of the speed at which air particles move at different temperatures (hot moves faster and cold moves slower). Since hot air moves faster, it takes up more space and, therefore, pushes against the air pressure of the room around to keep the can in its correct shape. By cooling the can down so quickly, the air particles cooled very fast, therefore crumbling under the faster moving air and its pressure around the can. This all caused the can to crush in on itself seconds after being placed on the water.
Another thing we did was to drink out of juice pouches and try to observe exactly how this happened. Our group, while confused at first, managed to get a somewhat accurate theory. We'd thought that, since our mouths made a seal, by sucking up the juice, the air pressure it the pouch pushed down on the juice, pushing it up the straw, and allowing the outside air pressure to squeeze the pouch. We were slightly off, as the correct explanation, as we found out, was that, by lowering the air pressure in our mouths, the higher air pressure outside squeezed the pouch, sending the juice up the straw. We all thought that was pretty interesting since neither of us had before thought of the mechanics of a juice pouch.
The last thing we did was learn how open and closed manometers worked. In closed manometers, there is gas in the "bubble" side of the U-shaped tube, mercury in the middle, ad a vacuum on the other end. The gas pressure is measured by determining how much higher the mercury is on one side than the other. One would subtract the height of the mercury on the vacuum side from the height of the gas side to get the difference. The difference is then your answer.
In an open manometer, one must first find the air pressure. They, once again, measure the height of both sides of mercury. To get a number, you subtract the higher number from the lower one. Then, if the mercury is higher on the open side, you add the difference to the air pressure measurement to get your final answer. If the mercury was higher on the gas side, you subtract the difference from the air pressure to get the answer.
