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## Using the Metric System

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**Using the Metric System**A. Why do scientists use the metric system? • The metric system was developed in France in 1795 - used in all scientific work because it has been recognized as the world wide system of measurement since 1960. • SI system is from the French for Le Systeme International d’Unites. • The metric system is used in all scientific work because it is easy to use. The metric system is based upon multiples of ten. Conversions are made by simply moving the decimal point.**What is the basic unit of length?**• The meter – a little longer than a yard**What do scientists use to measure the length of an object**smaller than a yard? • A centimeter – one hundredth of a meter, so there are 100 centimeters in a meter • A millimeter – There are 1,000 millimeters in a meter**How do scientists measure long distances?**• The kilometer – There are 1,000 meters in a kilometer**Base Units (Fundamental Units)**QUANTITY NAME SYMBOL _______________________________________________ Length meter m ----------------------------------------------------------------------------- Mass gram g ------------------------------------------------------------------------------- Time second s ------------------------------------------------------------------------------- Temperature Kelvin k -------------------------------------------------------------------------------- Volume(liquid)__________liter_____________L________________**SI Prefixes**Prefix Symbol Multiplication Factor Term Micro u (0.000 001) one millionth Milli m (0.001) one thousandth Centi c (0.01) one hundredth Deci d (0.1) one tenth One Unit 1 one Dekadk10 ten Hecto h 100 one hundred Kilo k 1000 one thousand Mega M 1 000 000 one million**Metric Units Used In This Class**QUANTITY NAME SYMBOL Length meter m centimeter cm millimeter mm kilometer km Mass gram g kilogram kg centigram cg milligram mg Volume liter (liquid) L (l) milliliter (liquid) mL (ml) cubic centimeter (solid) cm3**Derived Units**• Base Units – independent of other units-measure • Derived Units – combination of base units-calculated Examples • density g/L mass / volume (grams per liter) • volume m x m x m = meters cubed • Velocity m/s (meters per second**SCIENTIFIC NOTATION**• Scientific Notation: Easy way to express very large or small numbers • A.0 x 10x • A – number with one non-zero digit before decimal • x -exponent- whole number that expresses the number decimal places • if x is (-) then it is a smaller • if x is (+) than it is larger**PRACTICE**• Convert to Normal Convert to SN • 2.3 x 1023 m 3,400,000, 3.4 x 10-5 cm .0000000456**Multiplying**• Calculating in Scientific notation • Multiplying- • Multiple the numbers • Add the exponents • (2.0 x 104) (4.0 x 103) = 8.0 x 107**Dividing**• divide the numbers • subtract the denominator exponent from the numerator exponent • 9.0 x 107 3.0 x 102 • 3.0 x 105**Add**• Add or subtract • get the exponents of all # to be the same • calculate as stated • make sure the final answer is in correct scientific notation form • 7.0 x 10 4 + 3.0 x 10 3 = • 7. 0 x 104 + .3 x 104 = 7.3 x 104 • 70,000 + 3,000 = 73000= 7.3 x104**subtract**• 7.0 x 10 4 - 3.0 x 10 3 = • 7.0x 104 – .30 x 104 = 6.7 x 104 • 70,000 - 3 000 =67,000**PRACTICE**• Add: • 2.3 x 103 cm + 3.4 x 105 cm • Subtract: • 2.3 x 103 cm - 3.4 x 105 cm • Multiply: • : 2.3 x 103 cm X 3.4 x 105 cm • Divide: • : 2.3 x 103 cm / 3.4 x 105 cm**Significant figures**• http://www.youtube.com/watch?v=puvE8hF6zrY**Using Significant Figures (Digits)**• value determined by the instrument of measurement plus one estimated digit • reflects the precision of an instrument • example – if an instrument gives a length value to the tenth place – you would estimate the value to the hundredths place**Mathematical Operations Involving Significant Figures**Multiplication and Division The answer must have the same number of significant figures as the measurement with the fewest significant figures.**Making Unit Conversions**• Make conversions by moving the decimal point to the left or the right using: “ king henry died unitdrinking chocolate milk” Examples • 10.0 cm = __________m • 34.5 mL = __________L • 28.7 mg = __________kg**Factor label method /Dimensional analysis**• Use equalities to problem solve converting units. • quantity desired = • quantity given x conversion factor (equality) • A-given unit • B-desired unit • C-given unit • A x B • C B • C must equal 1 use equality sheet**Equalities You Need To Know**1 km = 1000 m 1 m = 100 cm 1 m = 1000 mm 1L = 1000 mL 1kg = 1000g 1 g = 100cg 1 g = 1000 mg**ENGLISH TO METRIC**• 1 inch=2.5 centimeters • 1 gal=3.8 liters • 1lb= 4.4 Newtons • 1qt = .94 Liters • 1 ft = .30 meters • 12 in = .30 meters • 1 mi = 1.6 Km**Four-step approach**When using the Factor-Label Method it is helpful to follow a four-step approach in solving problems: 1.What is question – How many sec in 56 min 2. What are the equalities- 1 min = 60 sec 3. Set up problem (bridges) 56 min 60 sec 1 min 4. Solve the math problem -multiple everything on top and bottom then divide 56 x 60 / 1**MotionDescribing and Measuring MotionHow do you recognize**motion? • An object is in motion when its distance from another object is changing • Movement depends on your point of view**Distance**We all know what the distance between two objects is... So what is it? What is distance? What is length? ALSO - you can't use the words "distance" or "length" in your definition; that would be cheating.**Distance**As you can see from your efforts, it is impossible to define distance. Distance is a fundamental part of nature. It is so fundamental that it's impossible to define. Everyone knows what distance is, but no one can really say what it is. However, distances can be compared.**Distance**We can compare the distance between two objects to the distance between two other objects. For convenience, we create standard distances so that we can easily make comparisons... and tell someone else about them. This doesn't define distance, but it allows us to work with it.**Distance**We'll be using meter as our standard for measuring distance. The symbol for distance is "d". And the unit for the meter is "m“. d = 0.2 m**Distance Activity**• Work in partners create a difference in position between you and a partner. Use a meter stick to determine the distance between you and your partner.( position A) • Now move to a different position. Measure the difference in your position now. ( Position B) make note of the distance you have traveled?**Time**Similarly, everyone knows what time is... But try defining it; what is time? Remember you can't use the word "time" or an equivalent to the word "time", in your definition.**Time**Like distance, time is a fundamental aspect of nature. It is so fundamental that it's impossible to define. Everyone knows what time is, but no one can really say what it is... However, like distances, times can be compared.**Time**We can say that in the time it took to run around the track, the second hand of my watch went around once...so my run took 60 seconds. When we compare the time between two events to the time between two other events, we are measuring time. This doesn't define time, but it allows us to work with it.**Time**We will be using the second as our standard for measuring time. The symbol for time is "t" The unit for a second is "s". t = 10s click here for a "minute physics" on measuring time and distance**Time Activity**Repeat previous distance activity Use a timer – use seconds as the unit • Determine the time it took to go from position A to position B Draw a diagram of your activity List the known information- Distance: between position A to position B Time: it took to go from A to B**How do scientists calculate speed?**• Speed – the distance the object travels in one unit of time • Rate – tells you the amount of something that occurs or changes in one unit of time • Speed = distance time**Speed**The units of speed can be seen by substituting the units for distance and time into the equation s = d t meters second m s We read this unit as "meters per second"**SPEED = Distance / time**• Use the information from the previous two activities to calculate your speed. • Use these steps • 1. draw a diagram • 2. list known and unknown data • 3. write the formula you will use • 4. plug in data • 5. solve the problem using the correct units**1**A car travels at a constant speed of 10m/s. This means the car: A increases its speed by 10m every second. c decreases its speed by 10m every second. c B C moves with an acceleration of 10 meters every second. c D moves 10 meters every second. c**2**A rabbit runs a distance of 60 meters in 20 s; what is the speed of the rabbit?**How can you calculate the distance an object has moved?**• Rearrange the speedformula • Speed = distance/time • Distance = Speed x Time**Rearrange the following formula**Speed =distance time Find-distance: what you do to one side you do to the other time x speed = distance x time time distance=time x speed Find- time: what you do to one side you do to the other distance= time x speed speed speed Time =distance speed**3**A car travels at a speed of 40 m/s for 4.0 s; what is the distance traveled by the car?**4**You travel at a speed of 20m/s for 6.0s; what distance have you moved?**5**An airplane on a runway can cover 500 m in 10 s; what is the airplane's average speed?**You travel at a constant speed of 20 m/s; how much time does**it take you to travel a distance of 120m? 6**7**You travel at a constant speed of 30m/s; how much time does it take you to travel a distance of 150m?**Graphing**• graph – a visual representation of data that reveals a pattern • Bar- comparison of different items that vary by one factor • Circle – depicts parts of a whole • Line graph- depicts the intersection of data for 2 variables • Independent variable- factor you change • Dependent variable – the factor that is changed when independent variable changes**Graphing**• Creating a graph- must have the following points • Title graph • Independent variable – on the X axis – horizontal- abscissa • Dependent variable – on Y axis – vertical- ordinate • Must label the axis and use units • Plot points • Scale – use the whole graph • Draw a best fit line- do not necessarily connect the dots and it could be a curved line.