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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.
Challenge
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.
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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!
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Ignacio's robotic car, Hyperion, traveled miles in hours. Emily's robotic car, Photon, traveled at an average speed of kilometers per hour. Which robotic car drove at a higher average speed?
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Discussion
Unit Ratio
A unit ratio is a ratio with a denominator of 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 unit.
The ratio for example, can be reduced by changing the numerator to foot. The ratio then becomes The units are omitted once they are the same. As a result, the ratio is reduced to Also, note that different ratios can be written using the same relationships.
The denominators of these ratios are different than unit. Divide both the numerator and denominator of each ratio by the number in the denominator. Then, the denominators will be equal to unit.
These resulting unit ratios mean that inch is approximately feet and minute is approximately hours. Unit ratios are useful when converting measurement units.
| Fact | is equal to | is equal to |
|---|---|---|
| Ratio |
Pop Quiz
Practice Rewriting Ratios
Write the given ratio in the indicated form.
Example
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.
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Notice the sign on the map's bottom right corner. This means that inch on the map corresponds to miles of actual distance at the school. How many miles does inches on the map represent in reality? Round the answer to three decimal places if necessary. {"type":"text","form":{"type":"math","options":{"comparison":"1","nofractofloat":false,"keypad":{"simple":true,"useShortLog":false,"variables":["x"],"constants":["PI"]},"rendered":false},"text":""},"formTextBefore":null,"formTextAfter":"miles","answer":{"text":["0.105"]}}
Hint
Write a ratio using the fact that inch on the map represents miles in real distance.
Solution
The goal is to find how many miles inches on the map represents in reality. This requires multiplying of an inch by a factor that converts inches to miles. Consider the given information on the map.
Write a ratio using this information. Since the given distance 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.
Now multiply inches by this ratio to get the distance in miles.
This means that inches on the map represent miles in real life.
Discussion
Conversion Factor
A conversion factor is a fraction where the numerator and denominator represent the same quantity with different units.
Recall that hour and 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 hours to minutes using the above conversion factor.
| Given Quantity | Conversion | Result |
|---|---|---|
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 If the task was to convert minutes to hours, minutes would be multiplied by this conversion factor.
| Given Quantity | Conversion | Result |
|---|---|---|
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 |
|---|---|---|
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 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.
Discussion
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.
The table shows the relationship between units of each measure type in the customary system.
Converting measures requires using the appropriate conversion factors.
| Customary Units | ||
|---|---|---|
| Type | Unit | Equivalent Unit |
| Length | foot (ft) | inches (in.) |
| yard (yd) | feet | |
| mile (mi) | feet | |
| Weight | pound (lb) | ounces (oz) |
| ton (T) | pounds | |
| Volume | cup (c) | fluid ounces (fl oz) |
| pint (pt) | cups | |
| quart (qt) | pints | |
| gallon (gal) | quarts | |
Example
Determining the Weight of the Robotic Car
The robotics competition that each team will join requires that the robotic cars weigh less than pounds. The robotic car designed by Ignacio's team, Hyperion, currently weighs 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 pound is ounces.
b Compare the answer from Part A with pounds.
Solution
a A conversion factor is needed to convert the given quantity from ounces to pounds. Recall how pounds and ounces are related.
b In Part A, the weight of the robotic car was found. It is equal to pounds, which is less than pounds.
Discussion
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.
In the metric system, multiples of units follow a decimal pattern. That is, they are powers of Other metric units are named by adding metric prefixes to the base units.
Note that each relationship in the tables can be written as a ratio. These ratios can be considered as conversion factors.
Metric Units of Length
The table shows the commonly used metric units of length.
| Unit | Equivalent Unit |
|---|---|
| millimeters (mm) | meter (m) |
| centimeters (cm) | meter |
| decimeters (dm) | meter |
| dekameter (dam) | meters |
| hectometer (hm) | meters |
| kilometer (km) | meters |
Metric Units of Capacity
For measuring capacity, the metric system uses the liter as the base unit.
| Unit | Equivalent Unit |
|---|---|
| milliliters (mL) | liter (L) |
| centiliters (cL) | liter |
| deciliters (dL) | liter |
| dekaliter (daL) | liters |
| hectoliter (hL) | liters |
| kiloliter (kL) | liters |
Metric Units of Weight
In the metric system, kilogram, gram, and milligram are some commonly used units for measuring weight.
| Unit | Equivalent Unit |
|---|---|
| milligrams (mg) | gram (g) |
| centigrams (cg) | gram |
| decigrams (dg) | gram |
| dekagram (dag) | grams |
| hectogram (hg) | grams |
| kilogram (kg) | grams |
Example
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 centimeters.
a Photon, Emily's team's robotic car, is 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 meter is centimeters.
b Compare the answer from Part A with centimeters.
Solution
a The given length is in meters. To convert from meters to centimeters, use the fact that meter is centimeters.
b The car has a length of centimeters. This is less than centimeters.
Discussion
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.
Example
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 | pounds | kilograms | inches | centimeters |
| Photon | pounds | kilograms | inches | centimeters |
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Hint
Remember, kilogram is about pounds and inch is 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.Finding A
The weight of Hyperion is pounds. In this case, the conversion factor should have a numerator in kilograms and a denominator in pounds.Cross out common units
Cancel out common units
CalcQuot
Calculate quotient
RoundDec
Round to decimal place(s)
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.Finding Missing Equivalents of Lengths
This part requires converting between inches and centimeters. At this point, it is useful to remember that inch is centimeters.Finding B
The length of Hyperion is inches. The conversion factor of will convert this length to centimeters.Finding D
Finally, Photon's length will be converted to inches. This calls for multiplication byCross out common units
Cancel out common units
CalcQuot
Calculate quotient
RoundDec
Round to decimal place(s)
Example
Speed of the Robotic Cars on an 80-foot Track
The robotics competition has finally come. Each team will race on an 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 minutes. Find the speed of the car in inches per second.
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b Photon completed laps in 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.
| Equivalent Quantities | Conversion Factor |
|---|---|
MultFrac
Multiply fractions
Cross out common units
Cancel out common units
Multiply
Multiply
CalcQuot
Calculate quotient
b It is given that Photon completes laps in minutes. Since a lap is feet, laps is equal to feet. With this information, the speed of the car can be found in feet per minutes.
| Equivalent Quantities | Conversion Factor |
|---|---|
MultFrac
Multiply fractions
Cross out common units
Cancel out common units
Multiply
Multiply
CalcQuot
Calculate quotient
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 | |
|---|---|---|
| Simplify |
As can be seen, Hyperion can travel feet in a second whereas Photon can travel 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 | |
|---|---|---|
Closure
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) | miles in hours |
| Photon (Emily's) | kilometers per hour |
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