Measurement and Precision

Measurement and Precision

Middle School

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Learning Objectives

• Define and differentiate between accuracy and precision in measurements.

• Identify units for length, capacity, and weight in Customary and Metric systems.

• Learn how to convert units within and between the Customary and Metric systems.

• Understand the concept of volume and how to measure it using a graduated cylinder.

Key Vocabulary

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Accuracy

Accuracy is how close a measurement comes to the true or actual value of an object.

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Precision

Precision shows how close multiple measurements are to each other, indicating consistent results every time.

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Customary System

This is the measurement system mainly used in the United States, with units like feet and pounds.

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Metric System

A decimal-based system used by scientists globally, with units like meters, grams, and liters.

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Volume

Volume measures the total amount of three-dimensional space that is taken up by an object.

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Meniscus

This is the curved upper surface of a liquid, read from the bottom for an accurate measurement.

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Accuracy vs. Precision

• Accuracy is how close a measurement is to the true or accepted value.

• ​For example, a scale showing 5.1 lbs for a 5 lb bag is accurate.

• Precision describes how specific a measurement is, like 4.25cm instead of 4cm.

• It also means getting consistent results, even if they are not accurate.

Multiple Choice

A student measures a book three times and gets the following results: 15.2 cm, 15.3 cm, and 15.2 cm. The actual length of the book is 18.0 cm. Which statement best describes the student's measurements?

• They are accurate but not precise.

• They are precise but not accurate.

• They are neither accurate nor precise.

• They are both accurate and precise.

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Systems of Measurement

Customary System

• This system of measurement is primarily used in the United States.

• Common units for length include inches and feet, and for weight include pounds.

• For measuring capacity or volume, this system uses units like cups and gallons.

Metric System

• This system is used by scientists and most countries around the world.

• It is a base-ten system, which makes conversions between units very simple.

• Common units include meters for length, grams for weight, and liters for capacity.

Multiple Choice

A scientist is recording the mass of a chemical sample for an international publication. Which system of measurement and unit would they most likely use?

• Customary System, using ounces.

• Customary System, using pounds.

• Metric System (SI), using gallons.

• Metric System (SI), using kilograms.

Customary System of Measurement

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Length

• The basic units for length are inch, foot, yard, and mile.

• There are 12 inches in a foot and 3 feet in a yard.

• A mile is much longer, with 5,280 feet or 1,760 yards.

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Weight

• Common units used for weight include the ounce, pound, and ton.

• It is important to remember that 1 pound equals exactly 16 ounces.

• For heavier objects, 1 ton is equal to a total of 2,000 pounds.

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Capacity

• Capacity measures volume with the fluid ounce, cup, pint, quart, and gallon.

• Key relationships are 1 cup has 8 fluid ounces and 1 pint has 2 cups.

• Also, 1 quart equals 2 pints, and 1 gallon equals 4 quarts.

Multiple Choice

According to the Customary System of Measurement, how many pints are in one gallon?

• 16 pints

• 8 pints

• 2 pints

• 4 pints

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What Is the Metric System?

• The metric system is based on the number ten, making conversions simple.

• ​The order of prefixes is: Kilo-, Hecto-, Deka-, Base Unit, Deci-, Centi-, Milli-.

• Remember this order with the phrase: King Henry Died By Drinking Chocolate Milk.

• Scientists use SI units like the meter (m), kilogram (kg), and second (s).

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Multiple Choice

Using the mnemonic 'King Henry Died By Drinking Chocolate Milk', if you are converting from kilometers to meters, how do you move the decimal point?

• Three places to the right

• Three places to the left

• One place to the right

• One place to the left

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Converting Between Measurement Systems

Multiple Choice

If you are given a conversion factor and asked to convert 6 cm to inches, what is the first step you should take?

• Divide the measurement by the conversion factor.

• Set up a proportion with the conversion factor and the given measurement.

• Immediately multiply 6 by the conversion factor.

• Guess the answer and check it.

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How Do We Measure Volume?

• Volume measures the amount of space an object or substance takes up.

• In a lab, use a graduated cylinder to measure a liquid's volume.

• Look for the meniscus, which is the curve at the liquid’s surface.

• For an accurate reading, use the very bottom of the meniscus.

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Multiple Choice

What is volume, and where should you read the liquid level on a graduated cylinder for an accurate measurement?

• How much space something takes up; read the bottom of the meniscus.

• How hot a liquid is; read any line on the cylinder.

• The length of an object; read the middle of the meniscus.

• The weight of a liquid; read the top of the meniscus.

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Common Misconceptions

Misconception	Correction
Accuracy and precision are the same thing.	Accuracy is being correct. Precision is being consistent.
Bigger metric units mean you multiply.	To convert to a larger unit, you divide by moving the decimal left.
Read a graduated cylinder at the liquid's edge.	Read the volume at the bottom of the curve, called the meniscus.
The Customary system is more accurate than the Metric system.	Both systems can be accurate. The Metric system is simpler for conversions.

Multiple Choice

How are the customary and metric systems of measurement different in their structure?

• There is no fundamental difference in their structure.

• The Customary system is based on tens, while the Metric system has irregular conversions.

• The Metric system is a base-ten system, while the Customary system uses non-uniform conversion factors (e.g., 12 inches in a foot, 3 feet in a yard).

• The Customary system is only for length, while the Metric system is only for volume.

Multiple Choice

A chef needs 2 gallons of milk for a recipe. The store only sells milk in quart containers. How many quarts does the chef need to buy?

• 16 quarts

• 4 quarts

• 6 quarts

• 8 quarts

Multiple Choice

If you convert 5,200 centimeters to kilometers, what is the result? (Hint: King Henry...)

• 0.52 km

• 5.2 km

• 520 km

• 0.052 km

Multiple Choice

A scientist is trying to determine the volume of a small, irregular rock. What is the best tool and method to use?

• Use a ruler to measure its length and width.

• Use a thermometer to measure its temperature.

• Place it on a scale to find its mass in grams.

• Use a graduated cylinder and the water displacement method.

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Summary

• Accuracy is correctness, while precision is consistency in measurements.

• The Customary System has unique conversions; the Metric system is based on ten.

• You can convert between systems by setting up a proportion.

• Measure liquid volume by reading the bottom of the meniscus in a graduated cylinder.

Poll

On a scale of 1-4, how confident are you about converting between different units of measurement?

• 1

• 2

• 3

• 4