Background: Suppose someone asked you to measure the area of your classroom in square cubits. What would you use? A cubit is an ancient unit of length equal to the distance from the elbow to the tip of the middle finger. Today, SI is used as a standard system of measurement.
Question: Why are standard units of measure important?
Materials water large graduated cylinder or beaker graph paper balance pieces of string spring scale rock samples ruler
Safety Precautions ^ El Ea tC
1. Read and complete the lab safety form.
3. Measure the weight and length of two rock samples using a nonstandard unit of measure. You might use your pinky, a paper clip, or anything you choose.
4. Record your measurements.
5. Working with a partner, explain your units of measure and which samples you measured. Ask your partner to measure the rocks using your units.
6. Record your partner's measurements.
7. Use the information in the Skillbuilder Handbook to design a data table in which to record the following measurements for each rock sample: area, volume, mass, weight, and density.
8. Carefully trace the outline of each rock onto a piece of graph paper. Determine the area of each sample and record the values in your data table.
Secure each rock with a piece of dry string. Place the string loop over the hook of the spring scale to determine the weight of each rock sample. Record the values in your data table. Pour water into a large graduated cylinder until it is half full. Record this volume in the table. Slowly lower the sample by its string into the cylinder. Record the volume of the water. Subtract the two values to determine the volume of the rock sample. Repeat Steps 9 and 10 for each rock. Make sure the original volume of water for each rock is the same as when you measured your first sample. Follow your teacher's instructions about how to use the balance to determine the mass of each rock. Record the measurements in your table.
1. Interpret How did the results of your initial measurements (Step 4) compare with your lab partner's (Step 6)? If they were different, why were they?
2. Propose What does this tell you about the importance of standard units of measure?
3. Compare the area of each of your samples with the volumes determined for the same rock. Which is the better measurement? Explain.
4. Calculate the density of each sample using this formula: density = mass/volume. Record these values in your data table.
5. Explain Does mass depend on the size or shape of a rock? Explain.
6. Identify the variables you used to determine the volume of each sample.
7. List the standard units you used in this investigation and explain the standard unit advantages over your measurement units.
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