1. The Scientific Method
Imagine a police investigation of a car accident. You are the detective. How would you figure out what happened?

2. Step 1: Make observations and collect data
Step 2: Form a Hypothesis (also called an educated guess) - I think this is what happened….
Step 3: Do experiments to test your hypothesis
Step 4: Revise hypothesis, if necessary, according to experimental data
Step 5: Draw a final conclusion: “This is what happened”

3. Accuracy and Precision

4. Accuracy:
Extent to which a measured value agrees with an accepted (true) value.
Factors that affect accuracy -
Human error
- avoid by taking several measurements
Method error
- avoid by using standardized methods
Example: error due to parallax
Parallax -
Shift of an objects apparent position when viewed
from different angles.
Avoid by proper maintenance and
calibration
Instrument error -
Examples: warping of meter stick
balance sticking or not calibrated

5. 8.4 cm Precision Degree of exactness or refinement of a measurement
Based on limitation of the instrument 8 9 cm
8.4 cm
Estimated digit
Read as

6. Consider 8 9 cm
Read as: 8. 4 2 cm
* Proper precision: record measurements to 1/10 of smallest
division on a scale
Meter stick or ruler: estimate to 1/10 of a mm
or 1/100 of cm

7. Consider cm 9 8
Read as: 8. 4 cm

8. Consider cm 9 8
Read as: 8. cm

9. - indicates how reproducible the results are.
Data Sets
Accuracy - How close a measurement or set of measurements are to a true or accepted value
Example: A student’s known height is cm.
Another student measures it as cm.
( not very accurate)
The nurse measures it as cm
( accurate)
Precision of a group of measurements:
How closely the measurements agree to one another.
- indicates how reproducible the results are.

10. Precise & Accurate Not Precise Not Precise Not Accurate
Analogy with shots at a target.
Precise &
Accurate
Precise
Not Accurate
Not Precise
Fairly Accurate
Not Precise
Not Accurate

11. True/Accepted Value: 21.00 cm
Group 1
Group 2
Group 3
21.00 cm
21.01 cm
21.02 cm
20.98 cm
21.00 cm
22.00 cm
18.00 cm
23.00 cm
17.50 cm
17.52 cm
17.48 cm
17.45 cm
17.51 cm
Avg
21.00 cm
21.00 cm
17.49 cm
Accurate and
precise
Accurate
not precise
Precise
not accurate

12. The following students measure the density of pieces of lead three times. The density of lead is actually
11.34 g/cm3. Identify the following sets of data as accurate or precise.
1) g/cm3, g/cm3, g/cm3
2) g/cm3, g/cm3, g/cm3
3) g/cm3, g/cm3, g/cm3