7. Convert Measurement Units
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Chapter 3
7.
Convert Measurement Units
Understanding measurement conversion is crucial in various fields, from engineering to daily life. The lesson emphasizes the importance of being proficient in converting units, especially within the metric system. It also delves into the concept of unit ratios, illustrating their practical applications like determining speed or converting dimensions of objects. This knowledge serves as a comprehensive guide for those involved in activities that require a nuanced understanding of unit conversions, making it easier to meet specific criteria or standards.
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Lesson Settings & Tools
| | 14 Theory slides |
| | 10 Exercises - Grade E - A |
| | Each lesson is meant to take 1-2 classroom sessions |
Convert Measurement Units
Slide of 14
Measuring is the process of using numbers to describe the physical properties of an object or space. Various units are used to measure. For example, many countries measure distance in kilometers, whereas others measure in miles. Converting these units to one another clears this difference. This lesson will teach how to convert measurement units.
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Different Measures: Comparing Average Speeds
Two student-led teams, one from Canada and the other the US, made remote controlled robotic cars. Ignacio, of the US, controls the his team's car — Hyperion. Emily, of Canada, controls her team's car — Photon. They are both participating in an international competition and are now doing a test run at the competition site.
Ignacio races the robotic car as fast as he can through classrooms, the mountain, around the lake, and finally finishes at the Theatre. Emily's follows a similar path but spends more time going through the mountains. How cool!
Ignacio's robotic car, Hyperion, traveled 0.4 miles in 2 hours. Emily's robotic car, Photon, traveled at an average speed of 0.4 kilometers per hour. Which robotic car drove at a higher average speed?
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Unit Ratio
A unit ratio is a ratio with a denominator of 1 unit. Every ratio can be rewritten as a unit ratio.
A ratio is a comparison of two quantities with similar units of measure. Consider writing unit ratios using the relationship between some units of measure. Notice that the denominator of each unit ratio is 1 unit.
The ratio 12 in. 1ft, for example, can be reduced by changing the numerator to 1 foot. The ratio then becomes 1 ft1ft. The units are omitted once they are the same. As a result, the ratio is reduced to 1. Also, note that different ratios can be written using the same relationships.
The denominators of these ratios are different than 1 unit. Divide both the numerator and denominator of each ratio by the number in the denominator. Then, the denominators will be equal to 1 unit.
These resulting unit ratios mean that 1 inch is approximately 0.083 feet and 1 minute is approximately 0.017 hours. Unit ratios are useful when converting measurement units.
| Fact | 1 foot is equal to 12 inches. | 1 hour is equal to 60 minutes. |
|---|---|---|
| Ratio | 1ft/12in. | 1h/60min |
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Practice Rewriting Ratios
Write the given ratio in the indicated form.
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Converting the Map's Distance to the Actual Distance
Ignacio relies on a GPS screen to help navigate his robotic car Hyperion through the school's diverse terrain. 
Notice the sign on the map's bottom right corner. This means that 1 inch on the map corresponds to 0.075 miles of actual distance at the school. How many miles does 1.4 inches on the map represent in reality? Round the answer to three decimal places if necessary.
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Hint
Write a ratio using the fact that 1 inch on the map represents 0.075 miles in real distance.
Solution
The goal is to find how many miles 1.4 inches on the map represents in reality. This requires multiplying 1.4 of an inch by a factor that converts inches to miles. Consider the given information on the map.
On the Map & & In Actual Distance 1in. & = & 0.075 mi
Write a ratio using this information. Since the given distance 1.4 is in inches and the goal is to convert it to miles, the denominator of the factor should also be in inches. Doing this ensures that the inches will cancel out. The numerator should contain the needed unit, which is miles.
1in. = 0.075 mi ⇓ 0.075 mi/1in.
Now multiply 1.4 inches by this ratio to get the distance in miles.
This means that 1.4 inches on the map represent 0.105 miles in real life.
1.4 in. * 0.075 mi/1in.
MoveLeftFacToNum
a*b/c= a* b/c
1.4 in. * 0.075 mi/1in.
Cross out common units
1.4 in.* 0.075 mi/1 in.
Cancel out common units
1.4 * 0.075 mi/1
Multiply
Multiply
0.105 mi/1
DivByOne
a/1=a
0.105 mi
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Conversion Factor
A conversion factor is a fraction where the numerator and denominator represent the same quantity with different units. Example Conversion Factor [0.5em] 60 minutes/1 hour Recall that 1 hour and 60 minutes represent the same quantity. Multiplying a quantity by a conversion factor changes the quantity to an equivalent quantity in different units. Examine how to convert 2 hours to minutes using the above conversion factor.
| Given Quantity | Conversion | Result |
|---|---|---|
| 2 hours | 2 hours * 60 minutes/1 hour | 120 minutes |
Although the final result is in minutes, both quantities represent the same amount of time. Note that the opposite conversion, from minutes to hours, has a conversion factor of 1 hour60 minutes. If the task was to convert 120 minutes to hours, 120 minutes would be multiplied by this conversion factor.
| Given Quantity | Conversion | Result |
|---|---|---|
| 120 minutes | 120 minutes * 1 hour/60 minutes | 2 hours |
As shown in the examples above, the process of including units of measurement as factors is called dimensional analysis. Dimensional analysis can also be used when deciding which conversion factor will produce the desired units. In the table, some common conversion factors are used to convert the given measures.
| Given Quantity | Conversion | Result |
|---|---|---|
| 3 pounds | 3 pounds * 16 ounces/1 pound | 48 ounces |
| 160 ounces | 160 ounces * 1 pound/16 ounces | 10 pounds |
| 1 mile | 1 mile * 1760 yards/1 mile | 1760 yards |
Some common conversions involve distance, mass, area, volume, time, and temperature.
Why
The Reason That the Quantities Are EquivalentThe numerator and denominator of the conversion factor represent the same quantity. That means their quotient equals 1. Then, by the Identity Property of Multiplication, the amount of the given quantity does not change when multiplied by the conversion factor.
When converting from one unit to another, the desired unit needs to be in the numerator of the conversion factor while the given unit needs to be in the denominator. That way when the quantity is multiplied by the conversion factor, the given unit will cancel out and the desired unit will remain.
Keep in mind that, despite the given quantity and the new quantity have different values, they represent the same amount.
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Customary System
The customary system is the system of measurement commonly used in the United States. This system of measurement contains units for length, capacity, and weight. For example, the inch is a unit of length, the ounce is a unit of weight, and the quart is a unit of volume. Examples of Units in the Customary System inch, ounce, and quart The table shows the relationship between units of each measure type in the customary system.
| Customary Units | ||
|---|---|---|
| Type | Unit | Equivalent Unit |
| Length | 1 foot (ft) | 12 inches (in.) |
| 1 yard (yd) | 3 feet | |
| 1 mile (mi) | 5280 feet | |
| Weight | 1 pound (lb) | 16 ounces (oz) |
| 1 ton (T) | 2000 pounds | |
| Volume | 1 cup (c) | 8 fluid ounces (fl oz) |
| 1 pint (pt) | 2 cups | |
| 1 quart (qt) | 2 pints | |
| 1 gallon (gal) | 4 quarts | |
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Determining the Weight of the Robotic Car
The robotics competition that each team will join requires that the robotic cars weigh less than 6 pounds. The robotic car designed by Ignacio's team, Hyperion, currently weighs 84 ounces.
a Find the weight of the robotic car in pounds.
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b Does the weight of this robotic car meet the requirement?
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Hint
a Write a conversion factor using the fact that 1 pound is 16 ounces.
b Compare the answer from Part A with 6 pounds.
Solution
a A conversion factor is needed to convert the given quantity from ounces to pounds. Recall how pounds and ounces are related.
84 oz * 1lb/16 oz
MoveLeftFacToNum
a*b/c= a* b/c
84 oz * 1lb/16 oz
Cross out common units
84 oz * 1lb/16 oz
Cancel out common units
84 * 1 lb/16
MultByOne
a * 1=a
84 lb/16
MovePartNumRight
a* b/c=a/c* b
84/16 lb
CalcQuot
Calculate quotient
5.25 lb
b In Part A, the weight of the robotic car was found. It is equal to 5.25 pounds, which is less than 6 pounds.
5.25 lb <6 lb This means that Ignacio's team is eligible to participate in the event.
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Metric System
The metric system is the system of measurement used in almost all countries. The base units in the metric system are meters for length, liters for capacity, and kilograms for weight. Base Units in Metric System meter, liter, and kilogram In the metric system, multiples of units follow a decimal pattern. That is, they are powers of 10. Other metric units are named by adding metric prefixes to the base units.
Metric Units of Length
The table shows the commonly used metric units of length.
| Unit | Equivalent Unit |
|---|---|
| 1000 millimeters (mm) | 1 meter (m) |
| 100 centimeters (cm) | 1 meter |
| 10 decimeters (dm) | 1 meter |
| 1 dekameter (dam) | 10 meters |
| 1 hectometer (hm) | 100 meters |
| 1 kilometer (km) | 1000 meters |
Metric Units of Capacity
For measuring capacity, the metric system uses the liter as the base unit.
| Unit | Equivalent Unit |
|---|---|
| 1000 milliliters (mL) | 1 liter (L) |
| 100 centiliters (cL) | 1 liter |
| 10 deciliters (dL) | 1 liter |
| 1 dekaliter (daL) | 10 liters |
| 1 hectoliter (hL) | 100 liters |
| 1 kiloliter (kL) | 1000 liters |
Metric Units of Weight
In the metric system, kilogram, gram, and milligram are some commonly used units for measuring weight.
| Unit | Equivalent Unit |
|---|---|
| 1000 milligrams (mg) | 1 gram (g) |
| 100 centigrams (cg) | 1 gram |
| 10 decigrams (dg) | 1 gram |
| 1 dekagram (dag) | 10 grams |
| 1 hectogram (hg) | 100 grams |
| 1 kilogram (kg) | 1000 grams |
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The Length of the Robot Car Designed by Emily’s Team
Ignacio's team discovered that their robotic car met the weight criteria. At the same time, Emily's team was putting another criterion to the test. The length criterion requires that the cars are no longer than 40 centimeters.
a Photon, Emily's team's robotic car, is 0.35 meters long. Write this length in centimeters.
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b Does this car meet the length criteria?
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Hint
a Write a conversion factor using the fact that 1 meter is 100 centimeters.
b Compare the answer from Part A with 40 centimeters.
Solution
a The given length is in meters. To convert from meters to centimeters, use the fact that 1 meter is 100 centimeters.
0.35 m * 100cm/1 m
MoveLeftFacToNum
a*b/c= a* b/c
0.35 m * 100cm/1 m
Cross out common units
0.35 m * 100cm/1 m
Cancel out common units
0.35 * 100 cm/1
DivByOne
a/1=a
0.35 * 100 cm
Multiply
Multiply
35 cm
b The car has a length of 35 centimeters. This is less than 40 centimeters.
35 cm < 40 cm It follows that Photon meets this criteria.
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Converting Measures Between Systems
Units in the customary system can be converted to units in the metric system and vice versa. This may necessitate recalling a lengthy list of conversion factors.
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Filling Out the Competition Application
Emily and Ignacio are filling out the application form for the robotics competition. They must enter the measurements of their cars in multiple system's units.
| Applications | ||||
|---|---|---|---|---|
| Name of Robotic Car | Weight | Length | ||
| Hyperion | 5.25 pounds | A kilograms | 15 inches | B centimeters |
| Photon | C pounds | 2.5 kilograms | D inches | 35 centimeters |
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Hint
Remember, 1 kilogram is about 2.2 pounds and 1 inch is 2.54 centimeters.
Solution
Notice that Hyperion's known measurements are in customary units, whereas Photon's known measurements are in metric units. Conversion between the systems is needed. The equivalent weights will be found first followed by the equivalent lengths.
Finding Missing Equivalents of Weights
The weights are in kilograms and pounds. Recall the relationship between these units. 1kilogram is about2.2pounds. or 1kg ≈ 2.2lb The required conversion factor will be obtained using this information.
Finding A
The weight of Hyperion is 5.25 pounds. In this case, the conversion factor should have a numerator in kilograms and a denominator in pounds. Conversion Factor Pounds → Kilograms [0.8em] 1kg/2.2lb After determining the factor, multiply the weight of Hyperion and the conversion factor.5.25 lb * 1kg/2.2 lb
MoveLeftFacToNum
a*b/c= a* b/c
5.25 lb * 1kg/2.2 lb
Cross out common units
5.25 lb * 1kg/2.2 lb
Cancel out common units
5.25 * 1 kg/2.2
MultByOne
a * 1=a
5.25 kg/2.2
MovePartNumRight
a* b/c=a/c* b
5.25/2.2 kg
CalcQuot
Calculate quotient
2.386363 ... kg
RoundDec
Round to 2 decimal place(s)
≈ 2.39
Finding C
To find the weight of Photon in pounds, the multiplicative inverse of the above conversion factor is needed. This is because the measurement in kilograms is converted to pounds. Conversion Factor Kilograms → Pounds [0.8em] 2.2lb/1kg Use this factor to find the equivalent weight in pounds.2.5 kg * 2.2lb/1 kg
MoveLeftFacToNum
a*b/c= a* b/c
2.5 kg * 2.2lb/1 kg
Cross out common units
2.5 kg * 2.2lb/1 kg
Cancel out common units
2.5 * 2.2 lb/1
DivByOne
a/1=a
2.5 * 2.2 lb
Multiply
Multiply
5.5 lb
Finding Missing Equivalents of Lengths
This part requires converting between inches and centimeters. At this point, it is useful to remember that 1 inch is 2.54 centimeters. 1inch is2.54centimeters. or 1in. = 2.54cm
Finding B
The length of Hyperion is 15 inches. The conversion factor of 2.54cm1in. will convert this length to centimeters. Conversion Factor Inches → Centimeters [0.8em] 2.54cm/1in. Multiply the length of Hyperion by this conversion factor to get the equivalent length in centimeters.15 in. * 2.54cm/1in.
MoveLeftFacToNum
a*b/c= a* b/c
15 in. * 2.54cm/1 in.
Cross out common units
15 in. * 2.54cm/1 in.
Cancel out common units
15 * 2.54 cm/1
DivByOne
a/1=a
15 * 2.54 cm
Multiply
Multiply
38.1 cm
Finding D
Finally, Photon's length will be converted to inches. This calls for multiplication by 1 in.2.54cm. Conversion Factor Centimeters → Inches [0.8em] 1 in./2.54cm Multiply 35 cm by 1 in.2.54cm.35 cm * 1 in./2.54cm
MoveLeftFacToNum
a*b/c= a* b/c
35 cm * 1in./2.54 cm
Cross out common units
35 cm * 1in./2.54 cm
Cancel out common units
35 * 1 in./2.54
MultByOne
a * 1=a
35 in./2.54
MovePartNumRight
a* b/c=a/c* b
35/2.54 in.
CalcQuot
Calculate quotient
13.779527 ... in.
RoundDec
Round to 2 decimal place(s)
≈ 13.78 in.
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Speed of the Robotic Cars on an 80-foot Track
The robotics competition has finally come. Each team will race on an 80-foot track. Opposing teams are watching live from their computers.
The live camera is not that good. The students watching decide to do some math to get a better idea of who is winning!
a Hyperion completed one lap in 5 minutes. Find the speed of the car in inches per second.
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b Photon completed 3 laps in 16 minutes. Find the speed of the vehicle in centimeters per second.
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c Which car will likely win?
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Solution
a The speed of an object is calculated by dividing the distance traveled by the amount of time spent traveling.
r = d/t Since one lap is 80 feet long and Hyperion travels a lap in 5 minutes, its speed can be written as follows. r = 80 ft/5min Notice that its unit is feet per minute. To convert this unit to inches per second, two conversion factors are needed.
| Equivalent Quantities | Conversion Factor |
|---|---|
| 1 ft = 12 in. | 12 in./1ft |
| 1 min = 60 sec | 1 min/60sec |
80ft/5 min * 12 in./1ft * 1 min/60sec
MultFrac
Multiply fractions
80ft * 12 in. * 1 min/5 min * 1ft * 60sec
Cross out common units
80 ft * 12 in. * 1 min/5 min * 1 ft * 60sec
Cancel out common units
80 * 12 in. * 1/5 * 1 * 60 sec
MultByOne
a * 1=a
80 * 12 in./5 * 60 sec
Multiply
Multiply
960 in./300 sec
CalcQuot
Calculate quotient
3.2 in./sec
b It is given that Photon completes 3 laps in 16 minutes. Since a lap is 80 feet, 3 laps is equal to 240 feet. With this information, the speed of the car can be found in feet per minutes.
r = 240 ft/16min To convert it to centimeters per second, two conversion factors are needed.
| Equivalent Quantities | Conversion Factor |
|---|---|
| 1 ft = 30.48 cm | 30.48 cm/1ft |
| 1 min = 60 sec | 1 min/60sec |
240ft/16 min * 30.48 cm/1ft * 1 min/60sec
MultFrac
Multiply fractions
240ft * 30.48 cm * 1 min/16 min * 1ft * 60sec
Cross out common units
240 ft * 30.48 cm * 1 min/16 min * 1 ft * 60sec
Cancel out common units
240 * 30.48 cm * 1/16 * 1 * 60 sec
MultByOne
a * 1=a
240 * 30.48 cm/16 * 60 sec
Multiply
Multiply
7315.2 cm/960 sec
CalcQuot
Calculate quotient
7.62 cm/sec
c In order to compare the speed of the cars, the information given at the beginning is sufficient. Make a table to show the speed of each car.
| Hyperion | Photon | |
|---|---|---|
| Speed = Distance/Time | 80 ft/5min | 240 ft/16min |
| Simplify | 16ft/min | 15ft/min |
As can be seen, Hyperion can travel 16 feet in a second whereas Photon can travel 15 feet per second. Therefore, Hyperion is faster. Alternatively, the answers found in Part A and Part B can be used. However, a conversion between inches and centimeters is required here.
| Hyperion | Photon | |
|---|---|---|
| Speed | 3.2in./sec | 7.62cm/sec |
To compare these quantities, use the fact that 1 inch is 2.54 centimeters. Multiply the speed of Hyperion by 2.54 cm1 in. to convert it to centimeters per second. 3.2in./1 sec * 2.54 cm/1 in. = 8.128cm/1 sec Hyperion traveled at 8.128 centimeters per second. That is greater than Photon's speed. It is likely that Hyperion will win this race!
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Different Measures: Comparing Average Speeds
Now take another look at this lesson's challenge comparing the average speeds of two robotic cars. This problem can be completed with the gained knowledge of converting different measurements. Make a table using the given information.
| Given | |
|---|---|
| Hyperion (Ignacio's) | 0.4 miles in 2 hours |
| Photon (Emily's) | 0.4 kilometers per hour |
0.4 km/1 h * 1mi/1.6 km
▼
Simplify
MultFrac
Multiply fractions
0.4 km * 1mi/1 h* 1.6 km
Cross out common units
0.4 km * 1mi/1 h* 1.6 km
Cancel out common units
0.4 * 1mi/1 h* 1.6
MultByOne
a * 1=a
0.4 mi/1.6 h
ReduceFrac
a/b=.a /1.6./.b /1.6.
0.25 mi/1 h
RoundDec
Round to 1 decimal place(s)
0.25 mi/1 h
Convert Measurement Units
Exercise 3.1
A painter needs 1 liter of paint to cover an area of 90 square feet. How many gallons of paint does the painter need to cover a room whose walls have an area of 100 square meters?
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We know that the painter uses 1 liter of paint to cover an area of 90 square feet. Let's express it as a rate. 90 ft^2/1L We want to find the number of gallons of paint it will take to cover a room whose walls have an area of 100 square meters. First, we will use 90 ft^21L to find out how many square feet the painter can cover with 1 gallon. To do so, remember the conversion factor between gallons and liter. Conversion Factor 3.79 L/1 gal Let's multiply the ratio by the conversion factor.
This ratio means that one gallon of paint covers about 341.1 square feet. We will multiply it by another conversion factor to convert square feet to square meters. We know that 1 square meter is about 10.76 square feet. Then, the conversion factor we need is the following. Conversion Factor 1 m^2/10.76 ft^2 Let's multiply 341.1ft^21 gal by this conversion factor.
This means that 1 gallon of paint covers about 31.7 square meters. Now, we will construct a ratio table for this relationship.
| Gallons | 1 | ||
|---|---|---|---|
| Square Meters | 31.7 |
We can divide each quantity by 31.7 to obtain a unit rate. This will helps us to calculate the gallons per 100 square meters.
| Gallons | 1 | 0.031 | |
|---|---|---|---|
| Square Meters | 31.7 | 1 |
Finally, we can multiply each quantity in the second row by 100.
| Gallons | 1 | 0.031 | 3.1 |
|---|---|---|---|
| Square Meters | 31.7 | 1 | 100 |
We got that 3.1 gallons of paint are needed to cover 100 square meters. Since the room has 4 walls, we need to multiply the 3.1 by 4 to obtain the total amount of paint. 4(3.1)≈ 12.4 Therefore, we need about 12.4 gallons of paint to cover a room whose walls have an area of 100 square meters.
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Convert Measurement Units
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