Today, our class went over the quiz about measurement and sig fig rules. Everybody messed up on the last part of the quiz so we got to retake it. We then completed the Density Lab that was unfinished from yesterday. We learned that the density of a regular solid and irregular solid. To get the density of a regular solid, you must first measure the mass of the solid using a scale. Second, you must measure the length, width, and height of the object using a ruler. Lastly, you take mass and divide it by the volume to get the density of that object. To get the density of an irregular solid, you must first measure the mass of the object using a scale (as you did for the regular solid) and record it. Second, you have to fill a 100 ml graduated cylinder half full of water and record the volume of water in the cylinder. Third, you gently place the object in the graduated cylinder. Fourth, you subtract the volume of the water and the object from the original volume of the water. Once you get your answer, you then divide the mass from the number you got and get the density of the object. The last thing we had to do sounds complicated but actually has nothing much to it at all. We had to figure out the density of a liquid. To do that, you have to first measure the mass of an empty 100 ml graduated cylinder. Second, fill the cylinder about 1/3 full. Third, measure the mass of the cylinder plus the liquid. Fourth, read the volume of the liquid in the cylinder. Fifth, subtract the mass of the cylinder and the liquid from the original volume of the liquid. Lastly, calculate the mass over the volume to get the density of the liquid.
Our class then learned all about unit conversion and dimensional analysis. We learned how to convert centimeters into yards, tons into kilograms, years to seconds, etc. Although this may seem like a lot of math, Mr. Paek showed us an easier way to figure out the problems other than taking the longer way, which consisted of much more effort. The easy way is to start by Writing out the units that you are given as a fraction. Second, you write out the units that you want at the end of the conversion as a fraction. Third, you determine the appropriate conversion factors such as yards, feet, inches, tons, miles, liters, seconds, etc. Finally, you evaluate the appropriate arrangement for conversion factors. That is, copy the conversion factors from step 3 into fraction form so that the units end up canceling. Remember that when you multiply fractions, you can cancel units only when they appear in the numerator of one fraction and the denominator of another. If you don’t get it at first, don’t get angry with yourself as it nearly just takes practice.
During the end of class, Mr. Paek showed us an experiment for all our hard work from unit conversion that literally was flaming. He showed us an example of density by taking a liquidly soap substance and making it into a bubble filled with a gas that was clearly flammable. The point of this experiment was to show that if the density of a gas were less than that of air, it would float. As Mr. Paek chose some volunteers to hold the bubble dispenser, which you had to keep shaking for the bubbles to come out, he then took a meter stick that had a candle on it and lit it with a match. As the bubbles rose, he would touch them with the flame of the candle and they would burst into flames. One time one of the bubbles actually flamed probably a little to close to the ceiling but nothing happened. Although the day was a lot of hard and complicated work, the period still turned out to be fun.
This post was really in depth, and did a good job explaining density, unit conversions, and the demo. The video was a good addition to the post.
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