1. Measurement in Science
Unit 1 Lesson 2 Lecture Notes

2. Essential Questions
1. What are the sources of uncertainty in measurement?
2. How do you record a measurement with the correct # of significant figures using both digital and non-digital equipment?

3. (1) Intro to Measurement
Because scientific theories are based on observation and experimentation, careful measurements are very important in science, especially in Chemistry

4. (1) Intro to Measurement
No measurement is perfect. All contain some degree of “built-in” uncertainty.
Limitations in precision of lab equipment
Estimation requires some subjective judgment
This leads to random error

5. (1) Intro to Measurement
You CAN’T
eliminate all uncertainty in measurement
You CAN
record measurements in a way that tells others how much uncertainty there is
It’s all about the number of digits we record

6. (2) Recording Measurements
How many digits should you record?
Record all “certain digits”
those for which there is a graduation (marking) on your instrument
Record one “estimated digit”
the digit that is between two graduations
can’t be measured directly so it must be estimated

7. (2) Recording Measurements
All measured digits + one estimated digit are collectively known as “significant figures” or “sig figs”

8. (2) Recording Measurements
Rulers, meter sticks, triple beam balances, graduated cylinders, and thermometers are a few of the instruments you might use in lab
Beakers and flasks are not used when precise measurements are needed, graduated cylinders or pipettes are better for precise measurement

9. (2) Recording Measurements
Step 1: determine the value of each increment on the measuring device
This ruler is labeled at every 1 cm
There are 10 lines between each 1 cm mark
Each line represents 0.1 cm (or 1 mm)

10. (2) Recording Measurements
Step 2 record all certain digits + one estimated digit
You can record with certainty 2.7 cm
The bar is about halfway between 2.7 and 2.8 cm
Record the length as 2.85 cm

11. (2) Recording Measurements
Give the length of the object shown using each ruler (unit = cm) Which ruler gives the most accurate measurement?
Ruler A: 6.2 cm
Ruler B: 62.2 cm A B
A. 6.2 cm
B cm

12. (3) How to Measure Liquid Volume
Measure from the bottom of the curved surface of the liquid (the meniscus) at eye level
Viewing at an angle will lead to inaccurate readings
In the illustration the volume is between 9.7 mL and 9.8 mL and you can estimate here to 0.1 mL since marks are given every 1 mL. Doing so gives a volume of 9.76 mL.

13. (3) How to Measure Liquid Volume
Step 1 : determine the value of each increment on the device
The cylinder is labeled at every 5 mL
There are 10 lines btwn each 5 mL mark
Each line represents 0.5 mL
Step 2: record all certain digits + 1 estimated digit
You can record with certainty 11.5 mL
Meniscus is right at the 11.5 mL mark
Record the volume as mL

14. (3) How to Measure Liquid Volume: practice reading each of the following
32.6 mL mL mL
32.6 mL
33.6 mL
8.46 mL A B C

15. (3) How to Measure Liquid Volume
The more graduations an instrument has, the more precise the measurements you can make with it
Always measure using the smallest possible device
e.g., if you are measuring 9 mL of fluid, use the 10 mL cylinder instead of the 100-mL cylinder

16. (4) The Volume of Solids
For regular shaped solids, measure the dimensions and apply these formulas:

17. (4) The Volume of Solids Calculate the volume of these objects.
Cylinder:
Volume of a cylinder = 3.14 x Radius x Radius x Length
Volume = 3.14 x Radius x Radius x Length
Radius = 4.5 x .5 = 2.25 inches
Length = = (.75 represents enclosure material thickness)
V = 3.14 x 2.25 x 2.25 x 10.75V =
cubic inches

18. (4) The Volume of Solids
For irregular shaped solids, use the water displacement method
The amount that the water level in the cylinder rises when the object is dropped in = the volume of the object
What is this cartoon’s volumn?

19. (4) The Volume of Solids
What is the volume of this dinosaur?

20. (5) Measuring with Digital Equipment
Some science lab equipment is digital
balance, pH meter, gas pressure probe, accelerometer
The rules for recording digital measurements are slightly different (but easier!)

21. (5) Measuring with Digital Equipment
The # on the digital display has one estimated digit included
Just record what you see on the display
The last digit may fluctuate. Choose the number that seems to “stick”

22. (5) Measuring with Digital Equipment
There is a special procedure for measuring mass on a digital balance that ensures you don’t include the mass of the container in your measurement
Never place items to be massed directly onto scale-always use a container

23. (5) Measuring with Digital Equipment
Turn scale on
Set mode to grams
Press “mode” until a “g” appears
Place empty container on platform
Never place item directly on balance.
Press “tare”
This will zero the balance so that the mass of the container will not be included in the readout.
Add substance to be weighed
Record displayed measurement
Last digit displayed is the estimated one
Last digit may flicker. Record the digit that the device seems to “prefer.”
Repeat twice and take average of 3 measurements.

24. Assessments
Measurement Worksheets
Measurement Lab