Objective: To Learn to Apply the Concept of Percent Error in Measuring

1. Objective: To Learn to Apply the Concept of Percent Error in Measuring ERROR in measuring = the difference between your measure and the actual or real measurement. It’s your mistake, with the units that you measured with. ACCURATE MEASURES = measurements close to the actual value PRECISE MEASURES = measures that are close together, they can be accurate, or not.

2. Imagine shooting darts at a board…

3. 3 Darts tightly together, but NOT near the center that you aimed for means you are PRECISE (close together) but not ACCURATE (close to perfect). Measures like this are good, you are doing a good job, the tool may be weak. X X X • 3 Darts all over the place means you are not precise, and you are not accurate. (you’re terrible at darts!) • Measures like this in science mean you are using a poor tool, and you are not using it well! X X X

4. Here, one dart is ACCURATE because it is close to the center target, but your darts show no close pattern, so they are NOT PRECISE. This is not good in science measuring, too random. X X X These three darts are close together, and they are close to the target center. These darts are both PRECISE and ACCURATE. In science we hope our measures are like this. X X X

5. Error is how close your measure is to accurate measuring. PERCENT ERROR is how close your measures are to actual, measured by percent. Example 1 You measure your text to be 12.5 inches tall, but it really is 11.9 inches tall. What is your error, what is your percent error? Error is easy: Error = 12.5 inches – 11.9 inches = 0.6 inches in error That is your “MISTAKE” in your measuring.

6. You measure your text to be 12.5 inches tall, but it really is 11.9 inches tall. What is your percent error? Measured Value – Actual Value Actual Value % Error = X 100% • MV – AV • AV • % Error = • X 100% • 12.5 inches – 11.9 inches • 11.9 inches • % Error = • X 100%

7. 0.6inches • 11.9 inches • % Error = • X 100% % Error = +5.04% Your measure was incorrect by about 5% and since the percent error was a positive number, your measure was OVER, or MORE THAN the actual. Percent error shows everyone how well you measured by proportion or percent, and if you measured too much, or too little. It’s a much better indicator of how well you measure.

8. Example 2 You estimate there are 325 pennies in a jar but there really are 317 pennies in there. What was your ERROR? What was your PERCENT ERROR?

9. Example 2 You estimate there are 325 pennies in a jar but there really are 317 pennies in there. What was your ERROR? What was your PERCENT ERROR? ERROR = 325 pennies – 317 pennies = 8 pennies • MV – AV • AV • % Error = • X 100% • 325 p – 317 p317 p • % Error = • X 100% % Error = + 2.52%

10. Example 3 You count 927 seeds and plant them. You sprout up 948 plants. What was your error and your percent error in counting seeds?

11. You count 927 seeds and plant them. You sprout up 948 plants. What was your error and your percent error in counting seeds? ERROR = 948 seeds – 927 seeds = 16 seeds • MV – AV • AV • % Error = • X 100% • % Error = • 927 s – 948 s948 s • X 100% • % Error = – 2.22% • Your measure is close, but UNDER the actual value, LESS THAN PERFECT.

12. You measure the temperature in the room to be 22.6°C but it is actually 23.7°C in the room. What is your error and your percent error?

13. Error = 23.7°C – 22.6°C = 1.1°C • MV – AV • AV • % Error = • X 100% • 22.6°C – 23.7°C23.7°C • % Error = • X 100% • % Error = – 4.64% • You measured under, and pretty close to actual.

14. Homework Finish the Temperature Lab report, careful with the math, it is due Tuesday, which is TOMORROW.