SI UNITS OF SCIENCE - Moore Public Schools



SI UNITS OF SCIENCE

(AKA METRICS)

Scientists all over the world use one system of measurement. This system is called the metric system. The official name of the metric system is Systeme Internationale d’Unites (international system of units), but is commonly abbreviated as SI.

The basic units of the SI system are meter, liter, and gram.

• The meter is used for linear measurements or measurements of length. In the United States, inches, feet, yards, or miles are commonly used for linear measurements. The symbol for meter is m.

• The liter is used for measuring volume. Today, in the United States, soft drinks are sold in liters instead of ounces, pints, quarts, or gallons. The symbol for liter is L.

• The gram is used to measure mass. The units on a triple beam balance are given in grams instead of ounces or pounds. The symbol for gram is g.

The metric system adds prefixes to these base units to make smaller or greater measurements. The prefixes are shown in the following table.

|PREFIX |PREFIX MEANING | |

| | |ABBREVIATION |

| | | |

| | |Length Mass Volume |

|giga |1 billion times the base unit |G |Gm |Gg |GL |

|mega |1 million times the base unit |M |Mm |Mg |ML |

|kilo |1000 times the base unit |k |km |kg |kL |

|hecto |100 times the base unit |h |hm |hg |hL |

|deka (deca) |10 times the base unit |da |dam |dag |daL |

|meter, gram, or liter |Base unit | |m |g |L |

|deci |1/10 of the base unit |d |dm |dg |dL |

|centi |1/100 of the base unit |c |cm |cg |cL |

|milli |1/1000 of the base unit |m |mm |mg |mL |

|micro |1 millionth of the base unit |µ |µm |µg |µL |

|nano |1 billionth of the base unit |n |nm |ng |nL |

These prefixes can be added to any of the metric base units. For example, the base unit for length is the meter. To measure smaller lengths, scientists can use centimeters. Based on the definition for centi, which is 1/100 of the base unit, a centimeter is 1/100 of a meter. There are 100 centimeters in a meter. The prefixes mean the same things no matter which base unit is being used. One kilogram would be 1000 times the base unit, which is the same as 1000 grams.

USING SI UNITS

Underline the root word (basic unit) for each of the following:

1. kilogram 4. millimeter

2. decimeter 5. decagram

3. hectometer 6. centimeter

Underline the prefix for each of the following:

1. kilogram 4. hectometer

2. deciliter 5. milligram

3. decameter 6. centiliter

Write the symbols for the following:

1. kilogram 4. decagram

2. deciliter 5. millimeter

3. hectometer 6. centiliter

Use the correct units to complete the story below.

Mary Metric went to a football game. She arrived late and had to sit on a narrow 15 centi__________ bench. She cheered as the quarterback threw a magnificent 50 __________ pass. Mary saw the large, 100 kilo__________ guard sack the quarterback. All this activity made Mary very thirsty. She bought a 0.5 __________ cola to quench her thirst. After the game, Mary had to walk one kilo__________ to get to her car. She arrived at her car only to find it stuck in a puddle with about 5.5 deca__________ of water. Mary knew she had to hurry home if she wanted to make her curfew. Luckily the football team came by and pushed the 7,000 kilo__________ car out of the mud. Mary felt the car hesitate and realized that she was out of gas. She stopped at the Jiffy store and added 7 __________ to her gas tank. Mary finally made it home, but was met at the door by her parents, who grounded her for being late. She also had to shovel 100 kilo__________ of manure onto their garden for expecting them to buy this alibi.

FINDING LENGTH

To measure length, we use a tool called a meter stick. For shorter lengths, a tool called a metric ruler can be used. Below you see a sample of the scale you will see on both the meter stick and the metric ruler. The length of an entire meter stick is one meter. It is divided into 100 parts called centimeters. A centimeter = .0l meter. These are the longer marks on the meter stick. They are usually numbered. The smallest marks on the meter stick are millimeters. There are 1,000 of these marks on each meter stick. A millimeter = .001 meter. Each centimeter is equal to ten millimeters. You could also say that a millimeter = .1 centimeter.

[pic]

Notice that the line measures more than 5, but less than 6 centimeters. If you were to measure this line to the nearest centimeter, You would say it is 6 centimeters long since it is closer to 6 cm than 5 cm. This is not very precise, however. You might say that the line measures 5 cm and 7 mm, but this is not convenient to record and it is considered bad form to mix metric units. Since each millimeter equals .1 cm, you might say that the line is 5.7 cm long. You might also say that the line is 57 mm long since there are 10 millimeters in each centimeter. Either way, you would be correct. Let’s see if you understand how to use a metric ruler to measure length.

DRAWING LENGTHS – Draw line segments the following lengths.

1. 64 mm

2. 13.5 cm

3. 10 cm 3 mm

4. 0.08 m

5. Draw a line two inches long and measure it to the nearest tenth of a cm. Include units with your answer.

MYSTERY OBJECT – Using the direction below, draw the mystery object.

1. Toward the bottom of this page, draw rectangle 1 with 27 mm sides and a 75 mm top and bottom.

2. Centered on the top of rectangle 1, draw a trapezoid with 24 mm sides, a 75 mm bottom, and a 40 mm top.

3. Centered in the right half of rectangle 1, draw rectangle 2 (see step four for dimensions) so it rests on the bottom line of rectangle 1 10 mm from the right side.

4. Draw rectangle 2 with 17 mm sides and a 12 mm top and bottom.

5. Centered in the left half of rectangle 1, draw rectangle 3 measuring 2 cm2.

6. Centered on the top line of your trapezoid, draw a square measuring 1 cm2.

MEASURING LENGTH

On the illustration below, find the length of the numbered lines. Place your answers on the lines below. Answers must be given in millimeters and centimeters.

[pic]

|Measurement # |Length in cm |Length in mm |Measurement # |Length in cm |Length in mm |

|1 | | |6 | | |

|2 | | |7 | | |

|3 | | |8 | | |

|4 | | |9 | | |

|5 | | |10 | | |

FINDING VOLUME –

VOLUME OF A FLUID

Earlier you were told that in science, we measure volume in liters. Volume is the amount of space occupied by matter. Usually when we think of volume, we think about liquids. There are other ways of calculating volume which will be discussed later.

To measure liquid The volume we use of a beaker or liquid is calculated by placing the liquid in a container (beaker, flask, graduated cylinder. The marks on these containers that indicate the number of milliliters are called graduations. When measuring a liquid in one of these containers, you should view the liquid at eye level as shown in the diagram. If you are using a graduated cylinder made of glass, you will notice that the upper surface of the liquid is curved or crescent-shaped. This curved surface is called a meniscus. The liquid volume should be read from the bottom of the meniscus. A plastic container will not have a meniscus. The volume is simply read from the level of the liquid. The volume of the liquid in the diagram is 35 mL., etc.) which has marking for measuring. Some containers measure more accurately than others as you will observe in the examples below. In science, fluids are usually measured in kL, L, or mL.

[pic]

You will notice that some containers measure more accurately than others as you will observe in the examples below. In the diagram above, the difference between one graduation and the next is two. This is known as the scale of the graduated cylinder. Determine and record the scale and correct volume for each example below. Make sure you include the correct unit when measuring the volume.

[pic]

A B C D

|Grad Cyl |A |B |C |D |

|Scale | | | | |

|Volume | | | | |

[pic]

A B C

|Beaker |A |B |C |

|Scale | | | |

|Volume | | | |

1. Which graduated cylinder measures liquids more accurately based on the scale you found for each one?

2. Which beaker measures liquids more accurately based on the scale you found for each one?

3. Is a graduated cylinder or a beaker more accurate or precise? Explain.

FINDING VOLUME – VOLUME OF A SOLID

To calculate the volume of a solid object, there are two methods. The first method is usually used to determine the volume of objects with geometrical shapes. To find the volume using this method, you would need to measure the dimensions of the object.

When calculating area (two dimensions), you multiply length and width (length x width). To calculate volume, you must add the measurement of a third dimension. The third dimension is called height. Therefore, when determining the volume of an object, you must multiply length, width, and height (length x width x height). The unit of volume for this method is cm3 (cm x cm x cm = cm3).

Using the information you just read: label the length, width, and height. Then, calculate the volume of the box. Show your work. Don’t forget to include the correct unit.

[pic] Volume = _______________

One thing to take note of is that it takes one milliliter to fill one cubic centimeter of space (1 cm3 = 1 mL). This means that these units are interchangeable.

[pic]

FINDING VOLUME – VOLUME OF AN IRREGULAR SHAPED SOLID

[pic]

How could you find the volume of the object (sphere) above? When you are trying to find the volume of an incomplete geometric shape such as the sphere above, there are two methods that can be used. The first is based on pure mathematical calculations. The second is called displacement. In science, we most often use displacement to find the volume of these irregular shaped objects.

When you place an object in a container of liquid, the level of the liquid rises. This happens because the object, which takes up space, pushes the water upward in the container. The amount of water that is displaced (rises upward) represents the volume of the object. The unit for this volume is often mL.

Using the information you just read, find the volume of the object below. Don’t forget to include the correct units.

[pic]

|Initial Volume (Liquid |Final Volume |Difference |

|Only) |(Liquid plus Object) |(Object Only) |

| | | |

CALCULATING MASS

It is important to know that there is a difference between mass and weight. Mass refers to the amount of matter an object has. Weight refers to the amount of force gravity exerts on an object. For most practical purposes the two are interchangeable and are treated as if they are the same, but it is important to keep in mind that there is a difference. As you know, the basic unit of mass is grams.

You will be using a triple beam balance to determine the mass of substances in class. It is called a triple beam balance because it has three beams or arms that support rider masses. The rider masses are moved horizontally until the pointer indicates that the mass of the riders and the substance are the same.

Each rider represents a different multiple for the basic unit gram. The larger rider usually represents increases of 100 grams per notch and is located at the back. The center beam usually has the rider that represents increases of 10 grams per notch. The third beam, usually has a rider that indicates both grams and decigrams. The grams are marked with number and the decigrams are the small lines in between. Remember that 1 gram = 10 decigrams.

The disc that holds the substance being massed is called the pan. The level indicator (pointer) is attached to the beams at the end opposite the pan. The level indicator moves vertically along the scale. When the level indicator is at zero on the scale, this indicates the balance is ready for use. Before you begin, use the zero adjusting knob to set the level indicator at zero if it is not already there. The zero adjusting knob will be located somewhere under the pan (ask your teacher if you are not sure).

Based upon what you just read, correctly label the parts of the triple beam balance pictured below.

[pic]

USING THE TIPLE BEAM BALANCE

To find the mass of a substance, you will use the following steps.

1. Place all the rider masses at zero on their beam.

2. Be sure the level indicator is a zero on the scale. Use the zero adjusting knob if necessary to reset the level indicator.

3. Place the substance to be massed on the pan.

4. Begin moving the largest rider mass one notch at a time until the level indicator moves below the zero on the scale.

5. When this happens, move the largest rider mass backward one notch and leave it.

6. Repeat the procedure from steps 4 and 5 for the second rider mass.

7. Now move the smallest rider mass forward one number at a time until the level indicator is at or below the zero on the scale.

8. If the level indicator is at zero on the scale, go on to step 10.

9. If the level indicator is below the zero on the scale, move it backward one line at a time until the level indicator rests at zero.

10. Determine the numerical value for each rider.

11. Add the values for all riders together. This is the mass.

Calculate and record the mass indicated on each set of beams pictured below. Don’t forget to include the correct unit.

[pic]

MEASURING METRIC TEMPERATURE

Temperature is a measure of the amount of heat contained in an object or substance. In the metric system, temperature is measured with a Celsius thermometer. Look at the Celsius thermometer pictured below. Observe the three standard temperatures marked on the scale; the temperature at which water boils (100( C), the temperature at which water freezes (0( C), and normal body temperature (37( C).

[pic]

The symbol ( means degree. The unit for measuring temperature in the metric system is

degrees Celsius (( C). The temperature 20( C, for example, should be read twenty degrees Celsius. A Celsius thermometer contains a liquid that rises and falls as the temperature changes. The temperature is read by looking at the mark on the scale that corresponds to the level of the liquid. It is important to determine the number of degrees represented by each mark so you can read the temperature accurately.

Look at the sample thermometers below and determine the temperature represented by each thermometer. Don’t forget to record your units!

[pic]

THINKING METRICALLY

"Give them a centimeter and they'll take a kilometer. “

"A gram of prevention is worth a kilogram of cure.”

As strange as these sayings may sound, one day you might be saying them! The United States is one of the few countries in the world that does not use the metric system exclusively. Scientists all over the world (including the United States) use the metric system to make scientific measurements. Increasingly, the metric system is being integrated into our lives. Most products we buy in the store list metric units along with the English units we are used to seeing on the label. It is very important that you begin to think metric. This means that instead of comparing metric units to the English units we are used to, we should practice getting a mental picture of approximately how much each metric unit represents without trying to compare.

Learning and using the metric system should not be viewed as a problem but rather as a solution to many problems. The metric system gives us easy to learn units for everyday use. It is much easier to convert from one type of unit to another in the metric system. Since the metric system is in base 10, multiplying and dividing are much easier in the metric system. Using the metric system will make communication and trade with other countries more convenient and profitable. Try the exercises that follow to see if you can think metric.

Which metric unit should you use to measure each of the following?

1. The amount of coffee in a coffee cup

2. How tall a house is

3. How hot it is on a summer day

4. The length of a pencil

5. Checking to see if you have a fever

6. The amount of water in a swimming pool

7. The mass of a friend

8. The width of a straw

9. The mass of a penny

10. The distance from Oklahoma City to Dallas

11. The length and width of a sheet of notebook paper

12. The length of a soccer field

13. The amount of gasoline a gas tank (car) will hold

14. The mass of a Hershey’s kiss

15. The amount of shampoo in a shampoo bottle

16. Amount of liquid medicine required for one dose

17. Size of a microscopic organism

CONVERTING METRIC MEASUREMENTS

Metric conversion means changing from one metric unit to another without changing the value (Example: changing from centimeters to meters). Remember that the metric system is based on units of ten. You must multiply or divide by ten or one of its multiples to convert from one unit to another.

A simple way to convert from one unit to another is to move the decimal to the right or the left depending on the unit to which you are converting. When multiplying by 10 or one of its multiples, the decimal always moves to the right. But when dividing by 10 or one of its multiples, the decimal always moves to the left.

For example, when converting kilometers to meters, you would move the decimal three places to the right because 1 kilometer is 1000 meters so you must multiply by 1000. When converting from millimeters to centimeters, you would move the decimal one place to the left because 1 millimeter is 1/10 of a centimeter so you must divide by 10.

PRACTICING CONVERTING METRIC MEASUREMENTS

PART A – To change millimeters (mm) to centimeters (cm), move the decimal one place to the left. Since 1 mm = 0.1 cm, you divide by 10 to convert.

Example: 63 mm = 6 3 . mm = 6.3 cm

Make the following conversions:

1. 56 mm = _______________ cm 6. 1 mm = _______________ cm

2. 9 mm = _______________ cm 7. 106.9 mm = _______________cm

3. 456 mm = _______________ cm 8. 493.8 mm = _______________cm

4. 19 mm = _______________ cm 9. 10 mm = _______________ cm

5. 7 mm = _______________ cm 10. 24 mm = _______________ cm

PART B – To change centimeters (cm) to meters (m), move the decimal two places to the left. Since 100 cm = 1 m, you divide by 100 to convert.

Example: 57 cm = 5 7 . cm = 0.57 m

Make the following conversions:

1. 27 cm = _______________ m 6. 1,267 cm = _______________ m

2. 6 cm = _______________ m 7. 13.5 cm = _______________ m

3. 15,473 cm = _______________ m 8. 27.03 cm = _______________ m

4. 123 cm = _______________ m 9. 143.76 cm = _______________ m

5. 54 cm = _______________ m 10. 793.5 cm = _______________ m

PART C – To change centimeters (cm) to millimeters (mm), move the decimal one place to the right. Since 1 cm = 10 mm, you multiply by 10 to convert.

Example: 2.4 cm = 2 . 4 cm = 24. mm = 24 mm

Make the following conversions:

1. 4.6 cm = ______________ mm 6. 789 cm = _______________ mm

2. .24 cm = _______________ mm 7. 34 cm = _______________ mm

3. 13 cm = _______________ mm 8. 1,234 cm = _______________ mm

4. 2.01 cm = _______________ mm 9. 0.653 cm = _______________ mm

5. 5 cm = _______________ mm 10. 0.8932 cm = _______________ mm

PART D – To change liters (L) to milliliters (mL), move the decimal three places to the right. Since 1 L = 1000 mL, you multiply by 1000 to convert.

Example: 1 L = 1 . L = 1 . 0 0 0 L = 1000 mL

Make the following conversions:

1. 59 L = _______________ mL 6. 8.3 L = _______________ mL

2. 0.6 L = _______________ mL 7. 0.077 L = _______________ mL

3. 4.5 L = _______________ mL 8. 6.221 L = _______________ mL

4. 349 L = _______________ mL 9. 17 L = _______________ mL

5. 1.24 L = _______________ mL 10. 0.321 L = _______________ mL

PART E – To change milliliters (mL) to liters (L), move the decimal three places to the left. Since 1000 mL = 1 L, you divide by 1000 to convert.

Example: 3200 mL = 3 2 0 0 . mL = 3 . 2 0 0 L = 3.2 L

Make the following conversions:

1. 4,789 mL = _______________ L 6. 326.5 mL = _______________ L

2. 899 mL = _______________ L 7. 25.95 mL = _______________ L

3. 79,500 mL = _______________ L 8. 0.5 mL = _______________ L

4. 56.2 mL = _______________ L 9. 590.3 mL = _______________ L

5. 0.625 mL = _______________ L 10. 8.50 mL = _______________ L

PART F – To change from grams (g) to milligrams (mg), move the decimal three places to the right. Since 1 g = 1000 mg, you multiply by 1000 to convert.

Example: 5 g = 5 . 0 0 0 g = 5 0 0 0 . mg = 5000 mg

Make the following conversions:

1. 96 g = _______________ mg 6. 3.9 g = _______________ mg

2. 2.4 g = _______________ mg 7. 0.043 g = _______________ mg

3. 0.45 g = _______________ mg 8. 3.554 g = _______________ mg

4. 882 g = _______________ mg 9. 85 g = _______________ mg

5. 29.9 g = _______________ mg 10. 925 g = _______________ mg

PART G – To change milligrams (mg) to grams (g), move the decimal three places to the left. Since 1000 mg = 1 g, you divide by 1000 to convert.

Example: 4800 mg = 4 8 0 0 . mg = 4 . 8 0 0 g = 4.8 g

Make the following conversions:

1. 3.250 mg = _______________ g 6. 990.2 mg = _______________ g

2. 211 mg = _______________ g 7. 32.85 mg = _______________ g

3. 12,500 mg = _______________ g 8. 0.7 mg = _______________ g

4. 50.8 mg = _______________ g 9. 311.9 mg = _______________ g

5. 0.14 mg = _______________ g 10. 4,278 mg = _______________ g

REVIEWING METRIC CONVERSIONS

List the metric prefixes in order from largest to smallest below.

________ ________ ________ Basic Unit ________ ________ ________

(m, L, g)

1. 63 cm = _______________ mm 20. 66,201 mL = _______________ kL

2. 17 cm = _______________ m 21. 2.47 L = _______________ mL

3. 42 mm = _______________ cm 22. 748.8 L = _______________ kL

4. 297.6 mm = _______________ m 23. 0.1716 kL = _______________ mL

5. 28 m = _______________ cm 24. 925 mL = _______________ cm3

6. 0.003 m = _______________ mm 25. 0.0005 kL = _______________ cm3

7. 13 cm = _______________ mm 26. 4.062 L = _______________ cm3

8. 13.5 cm = _______________ m 27. 77.5 mg = _______________ g

9. 3 mm = _______________ cm 28. 0.002 mg = _______________ kg

10. 1,798 mm = _______________ m 29. 6.755 g = _______________ mg

11. 76 m = _______________ cm 30. 30.9 g = _______________ kg

12. 1.9 m = _______________ mm 31. 0.065 kg = _______________ g

13. 2.04 cm = _______________ mm 32. 0.0129 kg = _______________ mg

14. 717.8 mm = _______________ m 33. 201 mg = _______________ g

15. 4.5 L = _______________ mL 34. 0.070 mg = _______________ kg

16. 442 L = _______________ kL 35. 88.25 g = _______________ mg

17. 0.06 kL = _______________ L 36. 0.0750 kg = _______________ mg

18. 0.373 kL = _______________ mL 37. 1.001 kg = _______________ g

19. 65.8 mL = _______________ L 38. 3.050 mg = _______________ kg

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