The Beginning Labs

Hello and welcome to my physics blog!  I'm Lisette LeMerise and this is my first blog entry of many to come. I hope that it all sounds okay.  During the first few weeks of school, my physics class has done multiple experiments.  In fact, my group has done exactly six. However, we have only discussed three of them together as a class.  The ones we discussed include the Hex Nut Lab, the Rod Lab, and Circle Lab #1 in that order.

Hex Nut Lab

For our starting lab, we did the Hex Nut Lab. We were asked, "What is the relationship between the number of hex nuts and the mass of the system?" and we were given multiple Petri dishes with different numbers of hex nuts inside.  However, we had one rule: Don't open the Petri dishes. With that one rule in mind, we started.  First, my group and I drew a predictive graph. We all agreed on a constant linear graph going in the upward direction, along with the prediction, "If the amount of hex nuts in the Petri dish increases, then the mass of the whole system will increase."

We decided to use a balance to measure the mass of the Petri dish with the hex nuts and count the number of hex nuts in each.  After it was all said and done, we recorded our data.  It is shown below left.

With this data, we soon graphed it (above right) and went into a class discussion.  We put all of our information on whiteboards and quickly started talking about the lab.


From our class discussion, my group concluded, "For every hex nut added to the dish, the overall mass increases by 7 grams."  As a class, we also realized that the slope of our graph was equal to the mass of an individual hex nut and that, if the hex nuts would have had more or less mass, the slope would have become more steep.  Along with that, we found a ratio between the number of nuts and the mass, giving it a direct linear relationship, and that the y-intercept of the graph (about 15 grams) was the mass of the Petri dish and the tape alone.

Rod Lab

For our second lab, we did the rod lab. For this investigation, we were given different size rods and we were asked, "Is there a relationship between the length of the rod and it's mass?"  We decided on having another linear graph as our predictive graph.  Then, we started our work.  To find the mass of the rod, we used a triple-beam balance.  Then, we traced the rods on their sides using graph paper and counted the number of cubes to find its length. Our data and graph is as follows:

Soon after, we had another class discussion.  This time, my group's conclusion came out as, "For every cube the length of the rod increases, the mass also goes up at a constant rate of 0.7 cubes.  It is also a direct, proportional, positive, and linear/constant relationship. " This time, we also learned the 5% rule from our teacher to see how good our data was. You take the y-intercept of your graph and divide by your largest y (in this case your largest mass) and then multiply by 100.  If it is under five percent, it's safe to assume you did a pretty good job. This time, our result was 3.9%.  We also learned that our points graph a ray, not a line because it can't be negative, and that the slope is how much the mass increases.

Circle Lab #1

For our last discussed lab, we did Circle Lab #1.  We were asked, "How does the diameter of a circle affect its circumference." and we were given different size circles.  To find the diameter, our group traced the circles on your average graph paper and counted the number of cubes across the middle.  To find the circumference, we put a string around the traced circles and measured, on graph paper, how much of the string was used. This way, we kept both of the units in cubes so they would be the same.  Our data and graph came out as follows:

Later, we had yet another class discussion.  For this lab, our group came up with the conclusion, "For every cube the diameter increases, the circumference goes up by 3.3314 cubes.  It goes up at a constant rate, causing a linear-style pattern."  We also did another 5% rule check, and our check came out to 0.07% which was even better than last time.  This time, as a class, we decided that the circumference of the circle should increase by pi for every cube of diameter added.  We also came to the conclusion that it would be useful to add the point (0,0) to our data because it logically makes sense in this situation and maybe others, and that logic does play a part in choosing our line of best fit.  Lastly, we concluded that if the y-intercept is off, it is usually systematic error, not human error.

Reflections

From these first couple of weeks, I have noticed that I talk at a moderate amount in class discussions.  That being said, I guess I could talk a little more, but only when I am really needed.  I also am doing what I think to be a fairly decent job in class.  I seem to be able to understand everything that's going on so far, although I'm still a little confused on how this class works.  This is mostly due to the fact that I have never learned in this style of science class before.  I even took a physics class last year, but it was nothing like this one.  I think that my group and I are doing pretty well, and I hope to learn more as the year goes on.