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Lesson Plans
Significant What?
Learning Activity
Focus for Media Interaction - Answer Key

Name: __________________________________

1. Watch the following segment and write down as many different kinds of measurement shown as possible. Be sure to record the units used.

Measurement Units Used
Gasoline Liters and gallons
Octane Octane
Air Pressure Pounds per square inch
Electricity Amperes
Wheel alignment Angles in degrees
Ignition voltage Volts
Engine speed Revolutions per minute (RPM)
Specific gravity No units
Spark plug gap Inches or mm
Exhaust particulates Parts per million (PPM)

2. Listen for the definitions of the term "measurement." What do they all have in common?

A measurement is a comparison of a known to an unknown. All measurements are composed of numbers and units. The number of digits used for the measurements is different.
3. Find out what the International Standards actually are, and where they are found in the United States?

The International Standards are found in a sub-basement of the National Institute for Standards and Technology outside Washington, D.C. The United States actually has both English and metric system standards in their reference set.

4. What is a significant figure, and how does it relate to the true measurement?

Discuss significant figures as being the number of places found on the instrument and one more place value that the student must estimate for themselves. This answer is not specifically given in the tape but may be inferred from the visuals and commentary. The number of significant figures then relates how close to the students will be able to come to the actual/true measurement of the item.

5. What must we do when we measure?

Check to make sure that your students realize that they should calibrate their instruments. This means they are checking the accuracy of the instrument.

6. What are the results of mercury poisoning?

The results of mercury poisoning are brain damage, blindness, weakened muscles, and death.

7. How does metallic mercury get into the food chain?

Bacteria change metallic mercury into methyl mercury that is water soluble. Since the mercury is now dissolved in the water, water organisms - fish, shellfish, plants - all absorb and store varying amounts of the methyl mercury over time. This causes a larger problem.

8. What is the USDA safe level for mercury and why is it necessary to keep the level so low?

The USDA safe level for mercury is 0.000001 or 1 ppm, one part per million. Biological concentration in fish tissue causes an increase in overall level as you move up the food chain.

9. Why do scientists do at least three measurements and take an average?

Scientists do at least three measurements because repeated measurements of the same sample are never the same; there is always a certain amount of error in the measuring procedure and the measuring instrument.

10. What is a true value?

The same value found by using different measuring instruments and procedures is accepted as the "true value."

11. What does "precise" mean? What is "accuracy"? Compare and contrast the concepts of precision and accuracy.

Accuracy is the measure of how close the average of your set of measurements comes to the "true value." The precision of your measurements is determined by how closely the measurements are clustered together.