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**Chapter 1 The Nature of Science**

Cubit: span from tip of middle finger to the elbow. Measure your seatmate’s height in cubits. Or measure back table length in cubits. Record measurements. How do they compare?

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**Standards of Measurement**

Accurate measurement is needed in a valid experiment. Standard—an exact quantity that people agree to use for comparison. In order for a measurement to make sense, it must include a number AND a unit. Examples: 150 ft, 35 cm, 64 mi

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Measurement Systems US: English system (pounds, feet, inches, Fahrenheit) Most other nations: metric system Science Worldwide: an improved version of the metric system called “International System of Units” or SI units. SI comes from the French Le Systeme Internationale d’Unites It is easier to convert units and share with others around the world.

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**The SI System SI Measurements and Base units**

Base unit for length is the meter (m) Converted unit: centimeter, kilometer Base unit for mass is the kilogram (kg) Converted unit: gram, milligram Base unit for time is the second (s) Converted unit: microsecond Base unit for electric current is the ampere (amp) Base unit for temperature is the kelvin (K) Base unit for volume is the liter (L)

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**The SI System Something Called SI**

The SI system is based on the number 10. Prefixes are used with the names of the units to indicate multiples of 10. Prefix multiplying factor kilo = 1000 (thousand) deci = 1/10 or 0.1 (tenth) centi = 1/100 or 0.01 (hundredth) milli = 1/1000 or (thousandth) micro = 1/1,000,000 or (millionth) nano = 1/1,000,000,000 or (billionth) Something Called SI

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**Derived Units Derived Unit: a unit that combines different SI units**

Common Derived Units: Area: cm2 or m2 Volume: cm3 or m3 Density: g/mL or g/cm3

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Transition

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**How can an aircraft carrier float?**

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**What is density? It is a derived unit.**

Density= mass divided by volume. How do you determine mass? Use a balance. Measure in grams or kilograms. Mr. Edmonds Rock to an Oldie

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**How do you determine volume?**

We will express volume in cm3 and mL. For a rectangular prism, V= L x W x H For a liquid, measure volume using a graduated cylinder . Find density first 90 seconds approximately no sig figs Base units Meters Liters and Grams focus on liters For a cube, volume = side cubed. For a sphere, volume = 4/3 pi x radius cubed. For a cylinder, volume is pi r squared x height.

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**Density=mass volume Because 1 cm3 = 1 mL Density=m (grams) = m (g)**

V (cm3) v (mL) Example: D=62.4 g/ (8.5 cm x 2.5 cm x 3.3cm)= D=62.4 g/ 70.1 cm3 = .9 g/ cm3 Wood floats in water because it has a lower density. An anchor sinks because the metal has a higher density than water. Helium balloons float because the density of the helium is lower than the density of the air. When the gas station tests the antifreeze in your car, they siphon some into a hydrometer. The hydrometer has objects in it that float in the liquid. By observing which objects float, it can be determined what the density of the liquid is, and if the chemicals are strong enough to retain the necessary freezing point.

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**Accurate Measurement Readings**

Read to the nearest mark, then estimate the number one decimal place further. 49.6 can be read with the lines on the ruler Estimate the last digit 4.4 can be read Estimate the last digit 6.1 can be read with the lines Estimate the last digit 49.66 cm 47.1 can be read with the lines on the ruler Estimate the last digit 47.10 cm

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Dimensional Analysis Sometimes things need to be converted to different units. You can use a conversion factor (a ratio) to change one unit to another. Ex. 1 in = 2.54 cm This process is called dimensional analysis

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**Conversion Process 5 Steps of Dimensional Analysis**

Start with the given (number & unit) X (times) Write the conversion factor as a fraction with the given unit on the bottom and new unit on top Cross out units that cancel Calculate & write the correct answer & units

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**Example: How many centimeters is 6.74 in?**

Start with the given (number & unit) X (times) Write the conversion factor as a fraction with the given unit on the bottom and new unit on top in = 2.54 cm Cross out units that cancel Calculate & write the correct answer & units 2.54 cm 6.74 in X = cm 1 in

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**Metric Conversions: The Ladder Method.**

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**How many jumps does it take?**

Ladder Method 1 2 KILO 1000 k 3 HECTO 100 h DEKA 10 da DECI 0.1 d Meters Liters Grams seconds CENTI 0.01 c MILLI m How do you use the “ladder” method? 1 – Determine your starting point. 2 – Count the “jumps” to your ending point. 3 – Move the decimal the same number of jumps in the same direction. 4 km = ________m Starting Point Ending Point How many jumps does it take? 4. 1 __. 2 __. 3 __. = 4000 m

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