1. MEASUREMENT
Using Measurements

2. A. Units
Scientists need a standard set of units when communicating information.
In 1960, an international committee of scientists met to update the existing metric system. This revised system was called the Systeme Internationale d’Unites (SI)

3. B. Base Units
There are seven base units in SI and they are as follows.
Quantity
Base Unit
Time
Second (s)
Length
Meter (m)
Mass
Kilogram (kg)
Temperature
Kelvin (K)
Amount of Substance
Mole (mol)
Electric Current
Ampere (amp)
Luminous intensity
Candela (cd)

4. B. Base Units

5. C. Temperature
When describing if something is hot or cold, it is useful to use temperature.
Fahrenheit is the temp scale used in the US
Water freezes at 32oF and boils at 212oF
Celsius is used throughout much of the rest of the world, especially in science.
Water freezes at 0oC and boils at 100oC

6. C. Temperature Conversions
The following equations are used for converting between Celsius and Fahrenheit.
oF = 1.8(oC) oC = (oF – 32)/1.8
Example. If the temperature is 41oC, what is it in Fahrenheit?

7. C. Temperature Conversions

8. C. Temperature Conversions
To convert between Celsius and Kelvin, use the following.
K = oC or oC = K - 273
Example. What is 451 K in Celsius?
Example. What is 21oC in Kelvin?

9. D. Derived Units
Not all quantities can be measured, some are calculated. When a combination of SI units are used, this is called a derived unit.
Volume is the space occupied by an object.
Vol = L x W x H (units cm3)
Density is amount per unit volume
Density = mass/volume Volume units g/mL or g/cm3

10. D. Density Calculations
Example. An object has a mass of 25.6 g and a volume of 18.3 mL. What is the density of the object?

11. D. Density Calculations
Example. A rectangular prism shown at right has a mass of 137 grams. What is its the volume and density?
8 cm
5 cm
3 cm

12. D. Density Calculations
If the object is irregularly shaped volume can be found by water displacement.
Example. The plastic fish shown at right has a mass of 11 grams. What is its volume? _____________________
What is its density? _____________

13. D. Density Calculations
Example. An object has a density of 3.14 g/cm3 and occupies 5.1 cm3. What is the mass of the object?
Example. Ethyl alcohol has a density of g/mL. What volume will 25.0 g occupy?

14. E. Accuracy vs. Precision
Accuracy - how close a measurement is to the accepted value
Precision - how close a series of measurements are to each other
ACCURATE = CORRECT
PRECISE = CONSISTENT

15. F. Significant Figures Indicate precision of a measurement.
Recording Sig Figs
Sig figs in a measurement include the known digits plus a final estimated digit
C. Johannesson

16. F. Significant Figures

17. F. Significant Figures Counting Sig Figs Count all numbers EXCEPT:
Leading zeros
Trailing zeros without a decimal point -- 2,500

18. Counting Sig Fig Examples
F. Significant Figures
Counting Sig Fig Examples
4 sig figs
3 sig figs
3. 5,280
3. 5,280
3 sig figs
2 sig figs

19. F. Significant Figures Calculating with Sig Figs
Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer.

20. F. Significant Figures Calculating with Sig Figs (con’t)
Add/Subtract - The # with the least number of decimal places determines the number of decimal places in the answer.

21. F. Significant Figures Calculating with Sig Figs (con’t)
Exact Numbers do not limit the # of sig figs in the answer.
Counting numbers: 12 students
Exact conversions: 1 m = 100 cm
“1” in any conversion: 1 in = 2.54 cm
C. Johannesson

22. F. Significant Figures Practice Problems 18.9 g - 0.84 g
(15.30 g) ÷ (6.4 mL)
18.9 g g

23. G. Scientific Notation 65,000 kg  6.5 × 104 kg
Converting decimal into Sci. Notation:
Move decimal until there’s 1 digit to its left. Places moved = exponent.
Large # (>1)  positive exponent Small # (<1)  negative exponent
Only include sig figs.
C. Johannesson

24. G. Scientific Notation 6.5 × 104 kg  65,000 kg
Converting Sci. Notation into decimal:
For positive exponent, move decimal to the right.
For negative exponent, move decimal to the left.
C. Johannesson

25. G. Scientific Notation Practice Problems 2,400,000 g 0.00256 kg
7  10-5 km
6.2  104 mm

26. G. Scientific Notation Calculating with Sci. Notation
(5.44 × 107 g) ÷ (8.1 × 104 mol) =