Recall that your expedition goal is to understand the importance of accurate and precise measurements
to help society. Now that you are fully briefed,
it is time to apply your understanding of measurement
to determine if certain measurement tools
meet a specified requirement.
We often take for granted that the tools we use to
measure objects are both accurate and precise. An
error of one millimeter may not mean much in the
classroom, but if it is your job to ensure that aircraft,
like space shuttles and airplanes, are assembled
correctly, one millimeter can cause losses of tens of
thousands of dollars. In modern airplane building,
the huge wings may be built in one factory, and other parts such as the body and the tail sections
built in another. If the scientists, engineers, and technicians in different factories do not use the
same unit of length, these expensive and critical parts may not fit together during assembly. Dan
Sawyer and other engineers at NIST work hard to ensure that measuring instruments sold in the
market are accurate.
Accurate measurements require accurate measuring tools, good measuring techniques, and a
thorough understanding of what factors can affect measurements. In the case of measuring
tapes, temperature and tension are two primary factors that affect the accuracy of measurements
performed. Tapes expand or grow in length when their temperature increases and shrink when the
temperature decreases. The amount of force or tension that is applied to the tape while it is in use
can also make measurements less accurate. If a tape stretches due to tension, the distances
between the graduations increase—making the tapes less accurate.
To begin this Field Assignment, you will examine the effect of temperature on the length of a
measuring tape. Once you have completed your examination, you will create a length-measuring
tool and analyze the effect of tension (expressed as a function of mass) on this tool in order to
make it more accurate.