1. Journal 2/1/16 Objective Tonight’s Homework
We know the number π to 10,000 decimal places or more. How do you think scientists and mathematicians measured it this well? What does π even mean?
Objective Tonight’s Homework
to learn the difference between accuracy and precision
p 67: WDYL 5, 7

2. Notes: Accuracy and Precision
We commonly use a dartboard as examples of accuracy and precision.

3. Notes: Accuracy and Precision
We commonly use a dartboard as examples of accuracy and precision.
Not precise Precise Not precise Precise
Not accurate Not accurate Accurate Accurate

4. Notes: Accuracy and Precision
Accuracy is a measure of how correct the number is. How close it is to the “real” value, or other accepted scientific measurements of the same thing.
On a dartboard, if you’re aiming for the middle, you’re only accurate if you hit it.

5. Notes: Accuracy and Precision
Accuracy is a measure of how correct the number is. How close it is to the “real” value, or other accepted scientific measurements of the same thing.
On a dartboard, if you’re aiming for the middle, you’re only accurate if you hit it.
Precision is a measure of how well you know your measurement. Saying, “school is 7.32 miles from my house” is more precise than saying “school is about 7 miles from my house.”
On a dartboard, precision is how consistent the throws are. How close they are to each other.

6. Notes: Accuracy and Precision
So how do we measure each of these? We can get accuracy through calibration.
If I take a thermometer and put it in boiling water, I can test to see if it measures 100 °C. If it does, I know it is accurate.

7. Notes: Accuracy and Precision
So how do we measure each of these? We can get accuracy through calibration.
If I take a thermometer and put it in boiling water, I can test to see if it measures 100 °C. If it does, I know it is accurate.
We get precision through more and more detailed tools. A meterstick with 1,000 little marks can give us higher precision than one with just 10.
Let’s talk about how to correctly show precision.

8. Notes: Accuracy and Precision
When taking measurements, we want to write the last certain number and the first uncertain one.
A “certain” number is usually the smallest labeled marks on a tool.
The “uncertain” number is usually a guess of how far the measurement is between the mark you just passed and the next one.

9. Notes: Accuracy and Precision
Example: Write the correct precision for the measurement of the item below.

10. Notes: Accuracy and Precision
Example: Write the correct precision for the measurement of the item below.
Our meterstick has markings down to millimeters, so our last certain point is 41.6 cm. It looks to be about halfway between 41.6 and 41.7, so our uncertain measurement is 0.05 mm. This gives us a total measurement of cm. This measurement shows proper precision.

11. Notes: Accuracy and Precision
One last thing to note:
If a measurement is right on a line, we say our “uncertain” measurement is “.0”.
Saying “35.0 m” is very different from saying “35 m”.
With the first one, we’re saying we could be off by 1/10 of a meter either way.
With the second, we’re saying we could be off by an entire meter either way!

12. Practicing Measurement
Your job for the rest of class is to grab a meterstick and measure the size of 10 objects in class. Measure down to the proper precision.
(E.C.) Measure 5 additional objects using a property different from length or size and with a different instrument than a meter stick.
Remember, we record the last certain number and the first uncertain one.
If you finish, you may start working on the homework.

13. Exit Question Which measurement below would be the most precise?
a) There are 2,000,000,000 grains of sand on the beach.
b) It is 1,943,020 feet from New York to L.A.
c) The pizza was cut into 8 slices that looked the same size
d) The runner finished the race with a time of 1 hour, minutes.
e) All of them sound about the same precision
f) None of these are really precise