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Section 1-4 Pgs. 22-25 Measurement and Safety 9-16-15 IN: How do scientists measure things? IN: How do scientists measure things?

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SI Measurement System International System of Units (SI) International System of Units (SI) Helps all scientists share and compare their observations and results. Helps all scientists share and compare their observations and results. The US by itself does not normally use the SI system of units The US by itself does not normally use the SI system of units

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SI System: EVERYWHERE ELSE Here in the United States we use MILES instead of KILOMETERS FARENHEIT instead of CELSIUS FEET instead of METERS KILOGRAMS instead of POUNDS (lbs)

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SI Measurement System

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Length Length is the long dimension of any object. Length is the long dimension of any object. Tool meter stick or ruler Tool meter stick or ruler SI Unit SI Unit Meter (m) Meter (m)

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Temperature A measure of how hot (or cold) something is. A measure of how hot (or cold) something is. Tool thermometer Tool thermometer SI Unit SI Unit Usually Celsius ( o C) Usually Celsius ( o C) Kelvin (K) Kelvin (K) K= C + 273.15 K= C + 273.15

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Mass The measurement of how much matter an object contains. The measurement of how much matter an object contains. Tool triple beam balance or scale Tool triple beam balance or scale SI Unit SI Unit Kilogram (Kg) Kilogram (Kg) Gram (g) Gram (g) 1 kilogram = 1,000 grams

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Weight The measurement of the force of gravity on you. The measurement of the force of gravity on you. Tool triple beam balance Tool triple beam balance SI Unit SI Unit Kilogram (Kg) Kilogram (Kg) Gram (g) Gram (g) 1 kilogram = 1,000 grams

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Weight or Mass? An object’s weight will change if you move it from Earth to the moon or to other planets, but its mass will stay the same. An object’s weight will change if you move it from Earth to the moon or to other planets, but its mass will stay the same.

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Volume The amount of space an object occupies. The amount of space an object occupies. Tool graduated cylinder Tool graduated cylindermeterstick SI Unit SI Unit Cubic meter (m 3 ) Cubic meter (m 3 ) Liter (L) Liter (L) Milliliter (mL)= 1 cc (cm 3 ) Milliliter (mL)= 1 cc (cm 3 )

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Measuring Volume Rectangular Objects Rectangular Objects Volume = Length x Width x Height Volume = Length x Width x Height

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Density The measurement of how much mass is contained in a given volume. The measurement of how much mass is contained in a given volume. It is also referred to how closely packed or crowded an object is. It is also referred to how closely packed or crowded an object is. Solids are the most dense. Solids are the most dense. Gases are the least dense. Gases are the least dense. Liquids are in between. Liquids are in between.

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Measuring Density Density=Mass/Volume (mass divided by volume) Tools: balance and graduated cylinder or meterstickUnits:g/L g/cm 3

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Density Facts Less dense object will “float” on top of more dense objects. Less dense object will “float” on top of more dense objects. For example, oil will float on water. For example, oil will float on water. Oil is less dense than water. Oil is less dense than water. Most of the time solids are more dense than liquids. Most of the time solids are more dense than liquids. Except for ice! Except for ice! 1g of water = 1 cc = 1 mL 1g of water = 1 cc = 1 mL (at standard temp and pressure) (at standard temp and pressure)

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Density Facts ALL samples of pure gold have a density of 19.3 g/cm 3. ALL samples of pure gold have a density of 19.3 g/cm 3. Fools gold has a density of 5.0 g/cm 3. Fools gold has a density of 5.0 g/cm 3.

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Accuracy and Precision They are not the SAME! They are not the SAME!

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What is accuracy? Accuracy - refers to the correctness of a measurement. Accuracy - refers to the correctness of a measurement. You are accurate if you hit the center of the bulls eye. You are accurate if you hit the center of the bulls eye.

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What is precision? You are precise if your arrow is close to other arrows. You are precise if your arrow is close to other arrows. You are accurate if your arrow is close to the bulls eye. You are accurate if your arrow is close to the bulls eye.

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Can you be both accurate and precise? Yes, if all your arrows are close together in the bulls eye. Yes, if all your arrows are close together in the bulls eye.

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What is precision? Precision - refers to how detailed a measurement is based on the measurement tool used. Precision - refers to how detailed a measurement is based on the measurement tool used. Using a meterstick to measure the thickness of one piece of paper is not going to give a very precise measurement. Using a meterstick to measure the thickness of one piece of paper is not going to give a very precise measurement.

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OUT:Explain the difference between accuracy and precision.

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