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Measurement and SI Units

Measurement and SI Units. Objectives – Students will be able to: Describe the difference between precision and accuracy Explain acceptable levels of error in measurement Determine the difference between an independent and dependent variable. Precision vs. Accuracy.

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Measurement and SI Units

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  1. Measurement and SI Units Objectives – Students will be able to: Describe the difference between precision and accuracy Explain acceptable levels of error in measurement Determine the difference between an independent and dependent variable

  2. Precision vs. Accuracy Consider the following three games of darts. How would you describe the the throws?

  3. Precision • Precision describes how close measurements are to one another. • Example: Five students measure the mass of an object on a balance and get the following values: • 560 g • 566 g • 568 g • 555 g • 559 g

  4. Accuracy • Accuracy describes how close a measurement is to the “true value.” • Example: Five students measure the mass of a 500 g mass on a balance and get the following values: • 507 g • 506 g • 499 g • 555 g • 501 g Who is the most accurate?

  5. Can you be one without the other? • Think of a situation in which you might be precise but not accurate. • Think of a situation in which you might be accurate but not precise. • Think of a situation in which you are both. • Think of a situation in which you are neither.

  6. Precision vs. Accuracy

  7. Acceptable levels of error • Q: What is an acceptable level of error in physics? • A: It depends on the situation!

  8. What about for our lab? • We would like to aim for less than 5% error in most of our measurements in a high school lab. • This amount will go down once you enter college and the workforce, particularly in engineering fields.

  9. Types of Error • Systematic • Consistent misreading of a measurement device • Miscalibrated or defective device • Instrument not “zeroed” • Can usually be detected and fixed • Random • Unknown and unpredictable • “Noise” in a system (common in physics due to electronics)

  10. Dependent vs. Independent Variables

  11. Other terminology • Independent variable is also sometimes called the explanatory variable • Dependent variable is also sometimes called the response variable

  12. Correlation • What does positive and negative correlation look like? What about no correlation?

  13. What measurement devices will we use in Physics 2? • Meter sticks and rulers • Thermometers • Balances • Timers or stopwatches • Accelerometers • Spring scales Just to name a few… Length Temperature Mass Time Acceleration Force

  14. SI Base Units

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