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19. Is the following sentence true or false? An answer is as precise as the most precise

measurement from which it was calculated.

Round the following measurements as indicated.

20. Round 65.145 meters to 4 significant figures.

21. Round 100.1°C to 1 significant figure.

22. Round 155 cm to two significant figures.

23. Round 0.000718 kilograms to two significant figures.

24. Round 65.145 meters to three significant figures.

3.2 Units of Measurement

Measurements are fundamental to the experimental sciences.

Lesson Summary

Using SI Units Scientists use an internationally recognized system of units to

communicate their findings.

The SI units are based on multiples of 10.

There are seven SI base units: second, meter, kilogram, Kelvin, mole, ampere, and

candela.

Prefixes are added to the SI units because they extend the range of possible

measurements.

Temperature Scales Temperature is a quantitative measure of the average kinetic energy

of particles in an object.

Scientists most commonly use the Celsius and Kelvin scales.

The zero point on the Kelvin scale is called absolute zero.

Kelvin-Celsius Conversion Equation is K = °C + 273.

One degree on the Celsius scale is the same as one kelvin on the Kelvin scale.

Density Density is a ratio that compares the amount of mass per unit volume.

The formula for density is density = [pic].

Density depends on the kind of material but not on the size of the sample.

The density of a substance changes with temperature.

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To convert degrees Celsius into kelvins:

add 273 to the °C.

To convert kelvins into degrees Celsius:

subtract 273 from the K.

Sample Problem Mercury melts at −39°C. What temperature is that in K?

To convert Celsius temperatures into Fahrenheit:

multiply the Celsius temperature by 9.

divide the answer by 5.

add 32.

Sample Problem Convert 40°C to °F.

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To convert Fahrenheit temperatures into Celsius:

subtract 32 from the Fahrenheit temperature .

multiply the answer by 5.

divide that answer by 9.

Sample Problem Convert 77°F to °C.

Now it’s your turn to practice converting temperatures.

1. Fill in the table below with the correct degrees.

After reading Lesson 3.2, answer the following questions.

Using SI Units

2. Complete the table showing selected SI base units of measurement.

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3. All metric units of length are based on multiples of .

4. The International System of Units (SI) is a revised version of the .

5. Explain what is meant by a “derived unit.”

6. Give at least one example of a derived unit.

7. Complete the following table showing some metric units of length. Remember that the

meter is the SI base unit for length.

Match each metric unit with the best estimate of its length or distance.

| 8. Height of a stove top above the floor |a. 1 km |

| 9. Thickness of about 10 sheets of paper |b. 1 m |

| 10. Distance along a road spanning about |c. 1 cm |

|10 telephone poles | |

| 11. Width of a key on a computer keyboard |d. 1 mm |

12. The space occupied by any sample of matter is called its .

13. Circle the letter of each sentence that is true about units of volume.

a. The SI unit for volume is derived from the meter, the SI unit for length.

b. The liter (L) is a unit of volume.

c. The liter is an SI unit.

d. There are 1000 cm3 in 1 L, and there are also 1000 mL in 1 L, so 1 cm3 is equal to

1 mL.

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Match each of the three descriptions of a volume to the appropriate metric unit of volume.

|Example |Unit of Volume |

|14. Interior of an oven |a. 1 L |

|15. A box of cookies |b. 1 m3 |

|16. One-quarter teaspoon |c. 1 mL |

17. A volume of 1 L is also equal to

a. 1000 mL

b. 1 dm3

c. 1000 cm

18. The volume of any solid, liquid, or gas will change with .

19. A kilogram was originally defined as the mass of .

20. Circle the letter of the unit of mass commonly used in chemistry that equals 1/1000

kilogram.

a. gram

b. milligram

c. milliliter

Match each unit of mass with the object whose mass would be closest to that unit.

|Mass |Unit of Mass |

|21. A few grains of sand |a. 1 kg |

|22. A liter bottle of soda |b. 1 g |

|23. Five aspirin tablets |c. 1 mg |

24. Is the following sentence true or false? The mass of an object changes with location.

25. When brought to the surface of the moon, will a mass have more or less weight than it

did on the surface of Earth, or will it be the same weight? Explain.

Temperature Scales

26. Draw an arrow below the diagram, showing the direction of heat transfer between two

objects.

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27. What properties explain the behavior of liquid-filled thermometers?

28. What are the two reference temperatures on the Celsius scale?

29. What is the zero point, 0 K, on the Kelvin scale called?

30. A change of temperature equal to one kelvin is equal to a change of temperature of

how many degrees Celsius?

31. Complete the diagram to show the reference temperatures in the Celsius and

Kelvin scales.

Density

32. Is the mass of one pound of lead greater than, less than, or equal to the mass of one

pound of feathers?

33. Which material has a greater density, lead or feathers?

34. How is density defined?

35. The mass of a sample is measured in grams, and its volume is measured in cubic

centimeters. In what units would its density be reported?

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36. Look at Table 3.6. Circle the letter of the material that will sink in liquid water at 4°C.

|a. aluminum |c. ice |

|b. corn oil |d. gasoline |

37. The density of a substance generally decreases as its temperature increases. Are there any

exceptions to this statement? Explain.

3.3 Solving Conversion

Problems

The numerical value of a measurement generally changes when

you convert from one system to another, but the actual amount of the quantity measured

does not change.

Lesson Summary

Conversion Factors Conversion factors are used to change a given measurement to some

other unit of measure.

A conversion factor is a ratio of equivalent measurements. It equals s 1.

Conversion factors have an unlimited number of significant figures. They are not

considered when rounding the answer.

Dimensional Analysis Dimensional analysis is a way to solve problems using the units,

or dimensions, of measurements.

Dimensional analysis problems can be done in one step or they can require several steps.

When using dimensional analysis, a measurement with one unit is changed to an

equivalent measurement with another unit.

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Essential Understanding

BUILD Math Skills

Converting Among Temperatures The Fahrenheit scale is

based on the melting point of ice (32 degrees above 0) and the

boiling point of water (212 degrees above 0). However, since

most of the rest of the world uses degrees Celsius, it is important

to be able to convert from units of degrees Fahrenheit to

degrees Celsius.

The SI base unit for temperature is Kelvin, or K. A temperature

of 0 K refers to the lowest possible temperature that can be reached.

−39°C + 273 = 234K

Add 273 to the °C.

40 x 9 = 360

360 ÷ 5 = 72

72 + 32 = 104ºF

Multiply the Celsius temperature

by 9.

Divide the answer by 5.

Add 32.

Subtract 32 from the Fahrenheit

temperature.

77 − 32 = 45

45 x 5 = 225

225 ÷ 9 = 25°C

Multiply the answer by 5.

Divide that answer by 9.

|Common Temperatures |

| |Fahrenheit (°F) |Celsius (°C) |Kelvin (K) |

|Water boils | |100 | |

|Human body |98.6 | | |

|Average room | | |293 |

|Water freezes |32 | | |

|Units of Measurement |

|Quantity |SI Base Unit |Symbol |

|Length | | |

|Mass | | |

|Temperature | | |

|Time | | |

|Metric Units of Length |

|Unit |Symbol |Factor Multiplying Base Unit |

|Meter |m |1 |

|Kilometer | | |

|Centimeter | | |

|Millimeter | | |

|Nanometer | | |

|lower |higher |

|temperature |temperature |

Celsius

100

divisions

Boiling point

of water

Freezing point

of water

100

divisions

Kelvin

Essential Understanding

Multi-Step Dimensional Analysis

|Change meters/second to kilometers/hour. | |

|Multiply by a conversion factor to |[pic] |

|change meters to kilometers: |[pic] |

|Multiply by a conversion factor to |or |

|change seconds to hours: |[pic] |

Notice that there usually is some choice in what conversion factors are used.

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