An error of this type is just as likely to be too high as it is to be too low. Newer pennies are actually almost entirely composed of zinc, but the thin coating of copper on the outside makes new pennies look very much like they are made of copper. If a systematic error affects all measurements in the same way, no amount of data, and no averaging can alleviate the bias. Figure 6 shows a scatterplot of mass versus year, demonstrating the change. They can then compare their findings to the expected results and use that to talk about the limitations of classroom equipment and small objects. See our lesson on to see how we built the micrometer. Precision is the closeness of a set of measurements.
First of all, attentive students may notice that the mass measurements for pennies tend to cluster around two separate values. In this case, the two faces of the micrometer are not exactly parallel; on one side the micrometer, where we made all the measurements, it measures a little too low and on the other side it measures too high. In the end, the uncertainty depends not only on your tool, but also on how you read it, and maybe many other factors in the environment. The 2 pennies were then placed in a graduated cylinder containing 20 mL of distilled water in order to find the volume of the pennies inside the water. If we assumed we were trying to measure the density of pure copper pennies, then including pennies minted after 1982 in the measurements would amount to a systematic error. The reason for this odd behavior is that in 1982 the U.
Some measurements will be too high, leading to positive deviations, and some measurements will be too low, leading to negative deviations. Overall, the results of the experiment were mostly reasonable. Record the initial water level of water as 50. The density of the unknown might be used to distinguish the unknown from other suspects. Measuring Density Experiment Date: 30 September 2010 Due Date: 8 October 2010 Is it a Copper Penny? Using your graphing calculator or LoggerPro, create a of y-axis versus x-axis for each metal. This plot can be used to introduce the concept of root mean square deviation as an error estimate. Placed t he 20 penn ies int o a grad uated cy linder 4.
The smallest increments on a micrometer scale probably correspond to a much smaller distance, and you might reasonably assume that the measurement uncertainty is correspondingly smaller. And last but not least, I will practice my expertise of determining densities of objects, as in this case, the pennies. Copper and zinc are different elements and therefore have different values. Accuracy is the closeness of measurements to the correct or accepted value. Record the initial of the and water.
In contrast, the uncertainty on the measurement of the diameter is only about 5% 0. We then switch to a Vernier caliper or a micrometer. Purpose: In this activi ty , I will determ ine the density of the metal used in U. Ask them what could make their results more accurate. The diameter of a penny is nominally 19.
Secondly, even if all the measurements are carefully made and there are no instrumental errors, we are still likely to get the wrong answer for the density. I will also repeat this three times and calculate the average. The procedures of this experiment will be easy. Learning Goals Students should learn how to measure mass and volume and how to compute density. Show them how to use the graduated cylinder correctly. An error of this type is just as likely to be too high as it is to be too low.
Record the final water level. In this case, the large size of the error suggests that it occurs in the most critical of the measurements: the thickness. This can be used to introduce or reinforce the ideas of technologies advances in the field of science. Context for Use This lesson is used to reinforce the teachings of density and the application to metals. Record the of the cylinder, water and the pennies. Older copper pennies should have a different of to density than zinc pennies. Teaching Notes and Tips This lab can also be developed as an inquiry lab Be careful dropping metal into a glass cylinder.
As they do this project, they design their own data table to show how they computed the density of a penny. Assuming you have pennies both older and younger than 1982 in your sample, you should see two peaks in the distribution: one at about 2. It amounts to about 30% uncertainty 0. Assuming all the pennies have the same thickness, the different measurements in figure 4 indicate a range of measurement errors, from about 0. For sample sizes of 6 measurements or more, the effect is usually smaller than 5%. Record the initial of the and water.
The notion of significant figures perhaps may also be utilized in this experiment. They can either make two plots a histogram of mass for pennies before 1982 and one for pennies after 1982 or they can come up with a way of plotting how mass depends on year. The means of this experiment will be to work with the density of pennies. We want to get the surface of the water to rise as much as possible when the pennies go in. Record the final water level.