Presentation is loading. Please wait.

Presentation is loading. Please wait.

Measurement and The Metric System

Similar presentations


Presentation on theme: "Measurement and The Metric System"— Presentation transcript:

1 Measurement and The Metric System

2 Standards of Measure One cubit ?

3 Standards of Measure

4 Standards of Measure When two people work together, they should both use the same standards of measure.

5 Standards of Measure September Another Nasa space craft, Mars Climate Orbiter, is lost as it arrives at the Red Planet. A mix-up over units for a key space craft operation is blamed - one team used English units while the other used metric.

6 SI Units

7 Derived SI Units

8 Prefixes for SI Units http://en.wikipedia.org/wiki/SI

9 Prefixes for SI Units

10 Metric System During the 1790s, a decimal system based on our number system, the metric system, was being developed in France. Easy to use Easy to remember Uses prefixes, that made the basic units larger or smaller by multiples or fractions of 10 For example: 1km = 1000 m = 10,000 dm = 100,000 cm 1 mi = 1760 yd = 5280 ft = 63,360 in The only country left behind is the USA.

11 Imperial and U.S. customary systems of measurement
Both the Imperial (UK and Canada) and U.S. customary systems of measurement derive from earlier English systems. Comparison of Imperial and U.S. volume measures 1 liquid U.S. gallon = litres ≈ Imperial gallon 1 Imperial gallon = litres ≈ liquid U.S. gallons On January 1, 1983, the metric systems and SI units were introduced in Canada.

12 Systems of Measurement
United States Customary System (USCS) Formally called British System Used in the US and Burma Length: foot Weight/force: pound Time: second Systeme International (SI) Also called the Metric or International System Used everywhere else in the world! In the last situation two units of measurement were mentioned. The first was the British unit and the second was metric units. Let’s first explore the British System, which is now called the USCS (united sates customary system). Used in US and Burma This is the system of measurement that they use in the US… due to our proximity we are all probably slightly familiar with this system. It uses foot as the unit of length, pound as the unit of weigh/force, and second as the unit of time. USCS is presently being replaced by the international system, especially in technology and science (in an attempt to avoid mistakes similar to the mars probe) and some sports, but I can’t imagine the day when we buy seat for a football game at 15.24meter line as oppose to the 50-yard line! Second line in the Sault will always be a mile from third line! SYSTEME INTERNATIONAL The metric system

13 Systeme International (SI)
Quantity Unit Symbol Length meter m Mass kilogram kg Time second s Force newton N Energy joule J Current ampere A Temperature kelvin K Here is a table of the SI units… some of them are probably extremely familiar to you, but lets take a moment and look at them together. Meter – Standard length of measurement for the metric system It was originally defined in terms of the distance from the north pole to the equator (thought to be close to 10,000km) – therefore a meter was 1 ten millionth of this. Now however, it is defined as being the length of the path traveled by light in a vacuum during a time interval of 1/299,792,458 of a second. What they pretty much did is keep relatively the same distance (ex. a meter) and come up with a new way to express it more accurately. Kilogram Is defined by a gram. The kilogram equals 100 grams; where a gram is the mass of 1 cubic centimeter of water at a temp. of 4 o Celsius. Second Only shared unit of time between USCS and SI. Was defined until recently as 1/86,400 of the mean (average) solar day. Each 24h/day, 60m/hour, 60s/min DO CALCULATION ON THE BOARD! Problem is that the Earth is gradually becoming slower, so instead they came up with a new definition based on the radiation produced by cesium-133. Newton Named after Sir Isaac Newton. Force required to accelerate 1 kilogram at 1m per second per second. In a few weeks we will be diving into the world of forces Joule The amount of work done by a force of 1 Newton active over a distance of 1meter. We will be looking at the Joule much closer when we look at Force/Distance Ampere The rate of flow of 1 coulomb of charge per second, where 1 coulomb is the charge of 6.25 X 10 to the 18 Kelvin Fundamental unit of temperature named after Lord Kelvin. 0oC is referred to as absolute 0 ~ where no molecular action can take place. For this class we will spend most of our time using the Celsius scale (= -273oc). The expectation is that you will be familiar the primary units of measurement for the SI system. I don’t expect you to memorize crazy figures, such as the ones we’ve just discussed, but I do expect that You know what the primary unit of measurement is for the Time (s), etc.

14 SI Conversions Major advantage – the decimal system – all digits are related to one another – multiples of 10! 1 kilometer = 1000 meters = 100,000 cm 1 meter = 100 cm = kilometer Major advantage – is that they use the decimal system (where all units are related to each other by either dividing or multiplying by 10. Sure, we’ll all seen stuff like this before and we often have to do conversions in daily life… everything from altering recipes, measuring deciding upon our schedules….. But if you really think about it… it’s sort of weird! Who in the world came up with the idea of measuring things in the first place and how did we finally get so advanced as to be able to measure totally precisely and so that each digit meant something in relation to the other digits… definitely crazy and something we take for granted. EUARIMUM THINGS!

15 Scientific Notation Scientists often use very large or very small numbers that can not be conveniently written as fractions or decimal fractions. For example, the thickness of an oil film on water is about m In scientific notation it is 1 x 10-7 m 0.1 = 1 x 10-1 0.001 = 1 x 10-3 10,000 = 1 x 104

16 Scientific Notation 0.1 = 1 x 10-1 0.001 = 1 x 10-3 10,000 = 1 x 104 Any number can be written as a product of a number between 1 and 10 and a power of 10. In general, M x 10n; Where M, is the a number between 1 and 10 and n, is the exponent or power of 10.

17 Decimal to Scientific Notation
578 = x 102 = x 10-2 3.5 = 3.5 x 100 Place a decimal point after the first nonzero digit reading from left to right. Place a caret (^) at the position of the original decimal point. The exponent of 10 is the number of places from the caret to the decimal point. If the decimal point is to the right of the caret, the exponent of 10 is a negative number. ^ ^ ^

18 Scientific Notation to Decimal
5.78 x 102 = 578 2.5 x = 0.025 3.5 x 100 = 3.5 Multiply the decimal part by the power of 10. Move the decimal point to the right by the exponent - If the exponent is a positive number Move the decimal point to the left by the exponent - If the exponent is a negative number Add zeros as needed.

19 Metric Length The basic SI unit of length is the metre (m).
Originally 1m = distance from the equator to either pole/10,000,000 “The metre is the length of path traveled by light in a vacuum during a time interval of 1/299,792,458 s Km m cm

20 Conversion Factor A conversion factor is an expression used to change from one unit to another. Expressed as a fraction whose numerator and denominator are equal quantities in two different units. The information necessary for forming a conversion factor is usually found in their conversion table as follows: 1 m = 100 cm So, the conversion factors are: 1 m and cm 100 cm 1 m

21 Conversion using Conversion Factor
So, convert 5m to cm: 5 m x 100 cm = 500 cm 1 m Where the unit of the denominator should be the same as the original unit, so they cancels out. So, convert 7 cm to m: 7 cm x 1 m = 0.07 m 100 cm

22 Conversion Factors as unit values
A conversion factor is an expression used to change from one unit to another. 1 m = 100 cm So, the conversion factors are: 1 m and cm 100 cm 1 m These conversion factors can be read as: per cm (or, 1 cm = m) per m (or, 1 m = 100 cm) 1 m 100 100 cm 1

23 Conversion using units value
Or, it can be converted as follows: 5 m = 5 x 1 m = 5 x 100 cm = 500 cm Similarly, 7 cm = 7 x 1 cm = 7 x m = 0.07 m 100 1 m = 100 cm 100 cm = 1 m Therefore, 1 cm = (1/100) m

24 Metric-English Conversion
To change from an English unit to a metric unit or from a metric unit to an English unit, we use a conversion factor, from the relation 1 in = 2.54 cm. So, the conversion factors are: 1 in and cm 2.54 cm 1 in

25 Area The area of a plane surface is the number of square units that it contains. To measure the surface area of an object, you must first decide on a standard unit of area. Standard units of area are based on the square of standard lengths, for example 1 square m.

26 Area Find the area of a rectangle 5 m long and 3 m wide.
By simply counting the number of squares, we find the area of the rectangle is 15 m2. Or, by using the formula A = l x w = 5 m x 3 m = (5 x 3) (m x m) = 15 m2

27 Volume The volume of a figure is the number of cubic units that it contains. Standard units of volume are based the cube of standard lengths, such as cubic meter, cubic cm, cubic in.

28 Volume Find the volume of a rectangular prism 6 cm long, 4 cm wide, and 5 cm high. To find the volume of the rectangular solid, count the number of cubes in the bottom layer and then multiply by the number of layers. Or, V = l w h = 6 x 4 x 5 cm x cm x cm = 120 cm3

29 Mass The mass of an object is the quantity of material making up the object. One unit of mass in the metric system is the gram (g). The gram is defined as the mass of 1 cm3 of water at its maximum density (at 4 C). Since the gram is so small, kg is the basic unit of mass in SI (Système international d'unités) .

30 Weight The weight of an object is a measure of the gravitational force or pull acting on an object. The weight unit in the metric system is the newton (N). An apple weighs about one newton. A newton is the amount of force required to accelerate a mass of one kilogram by one meter per second squared. 1 N = 1 kg·m/s² The pound (lb), a unit of force, is one of the basic English system units. It is defined as the pull of the earth on a cylinder of a platinum-iridium alloy that is stored in a vault at the U.S. Bureau of Standards. 1 N = lb 1 lb = 4.45 N

31 kg with weight When the weight of an object is given in kilograms, the property intended is almost always mass. Occasionally the gravitational force on an object is given in "kilograms", but the unit used is not a true kilogram: it is the deprecated kilogram-force (kgf), also known as the kilopond (kp). An object of mass 1 kg at the surface of the Earth will be subjected to a gravitational force of approximately newtons (the SI unit of force).

32 Time The basic unit of time is second (s) in both system.
It was defined as 1/86400 of a mean solar day. Now the standard second is defined more precisely in terms of frequency of radiation emitted by cesium atoms when they pass between two particular states; that is, the time required for 9,192,631,770 periods of this radiation.

33 Electrical Units The ampere (A) is the basic unit and is measure of the amount of electric current. Derived units are: Columb (C) – is a measure of the amount of electrical charge Volt (V) – is a measure of electric potential Watt (W) - is a measure of power

34 Accuracy vs. Precision Accuracy: A measure of how close an experimental result is to the true value. Precision: A measure of how exactly the result is determined. It is also a measure of how reproducible the result is. Absolute precision: indicates the uncertainty in the same units as the observation Relative precision: indicates the uncertainty in terms of a fraction of the value of the result

35 Accuracy Physicists are interested in how closely a measurement agrees with the true value. This is an indication of the quality of the measuring instrument. Accuracy is a means of describing how closely a measurement agrees with the actual size of a quantity being measured.

36 Error The difference between an observed value and the true value is called the error. The size of the error is an indication of the accuracy. Thus, the smaller the error, the greater the accuracy. The percentage error determined by subtracting the true value from the measured value, dividing this by the true value, and multiplying by 100.

37 Error

38 Significant Digits The accuracy of a measurement is indicated by the number of significant digits. Significant digits are those digits in the numerical value of which we are reasonably sure. More significant digits in a measurement the accurate it is:

39 Significant Digits More significant digits in a measurement the accurate it is: E.g., the true value of a bar is 2.50 m Measured value is 2.6 m with 3 significant digits. The percentage error is ( )*100/2.50 = 4% Measured value is 2.55 m with 3 significant digits. The percentage error is ( )*100/2.50 = 0.2% Which one is more accurate? The one which has more significant digits

40 Rules for Determining “Significant Digits”
All non zero digits are significant All zeros between significant non zero digits are significant  5 significant digits A zero in a number (> 1) which is specially tagged, such as by a bar above it, is significant. 250,000  3 significant digits Zeros at the right in whole number  2 significant digits All zeros to the right of a significant digits and a decimal point  7 significant digits Zeros at the left in measurements less than 1 are not significant  5 significant digits

41 Determine the “Accuracy” and “Precision”
3463 m 4 S.D.s 1m 3005 km  8800 V km kg g A cm g 6 SDs g m m

42 Precision Being precise means being sharply defined.
The precision of a measuring instrument depends on its degree of fineness and the size of the unit being used. Using an instrument with a more finely divided scale allows us to take a more precise measurement.

43 Precision The precision of a measuring refers to the smallest unit with which a measurement is made, that is, the position of the last significant digit. In most cases it is the number of decimal places. e.g., The precision of the measurement 385,000 km is 1000 km. (the position of the last significant digit is in the thousands place.) The precision of the measurement 0.025m is 0.001m. (the position of the last significant digit is in the thousandths place.)

44 How precise do we need? Physicists are interested in how closely a measurement agrees with the true value. That is, to achieve a smaller error or more accuracy. For bigger quantities, we do not need to be precise to be accurate.

45 How precise do we need? For bigger quantities, we do not need to be precise to be accurate. E.g., the true value of a bar is 25 m Measured value is 26 m with 2 significant digits. The percentage error is (26-25)*100/25 = 4% E.g., the true value of a bar is 2.5 m Measured value is 2.6 m with 2 significant digits. The percentage error is ( )*100/2.5 = 4% Which one is more precise? The one which has the precision of 0.1m Which one is more accurate? Both are same accurate as both have 2 significant digits

46 Accuracy or Relative Precision
An accurate measurement is also known as a relatively precise measurement. Accuracy or Relative Precision refers to the number of significant digits in a measurement. A measurement with higher number of significant digits closely agrees with the true value.

47 Estimate Any measurement that falls between the smallest divisions on the measuring instrument is an estimate. We should always try to read any instrument by estimating tenths of the smallest division.

48 Accuracy or Relative Precision
In any measurement, the number of significant figures are critical. The number of significant figures is the number of digits believed to be correct by the person doing the measuring. It includes one estimated digit. A rule of thumb: read a measurement to 1/10 or 0.1 of the smallest division. This means that the error in reading (called the reading error) is 1/10 or 0.1 of the smallest division on the ruler or other instrument. If you are less sure of yourself, you can read to 1/5 or 0.2 of the smallest division.

49 Estimate to 1/10th of a cm What should be the estimated value?
L = 6.7 cm

50 Estimate to 1/10th of a mm What should be the estimated value? L = ?
1 cm L = ?

51 6 or 6.0 cm? What should be the estimated value? 1 cm L = ?

52 Estimate to 1/10th of the smallest unit

53 Estimate to 1/10th of the smallest unit
What should be the estimated value? 1 cm L = ?

54 Estimate to 1/10th of the smallest unit
The estimated value is x unit value = 0.7 x 1 cm = 0.7 cm 1 cm L = cm = 6.7 cm

55 Estimate to 1/10th of the smallest unit
What should be the estimated value? 1 cm L = ?

56 Estimate to 1/10th of the smallest unit
The estimated value is x unit value = 0.7 x 0.1 cm = 0.07 cm 1 cm L = 6.7 cm cm = 6.77 cm

57 Estimate to 1/10th of the smallest unit
0 2 cm What should be the estimated value? L = ?

58 Estimate to 1/10th of the smallest unit
0 2 cm The estimated value is x unit value = 0.7 x 2 cm = 1.4 cm L = cm = 13.4 cm

59 Estimate to 1/10th of the smallest unit
cm What should be the estimated value? L = ? ?

60 Estimate to 1/10th of the smallest unit
cm The estimated value is x unit value = 0.7 x 0.25 cm = cm L = cm = cm ?

61 Measurement An object measured with a ruler calibrated in millimeters. One end of the object is at the zero mark of the ruler. The other end lines up exactly with the 5.2 cm mark. What reading should be recorded for the length of the object? Why?

62 Precision Which of the following measured quantities is most precise?
Why? 126 cm 2.54 cm 12.65 cm 48.1 mm 0.081 mm

63 Exact vs. Approximate numbers
An exact number is a number that has been determined as a result of counting or by some definition. E.g., 41 students are enrolled in this class 1in = 2.54 cm Nearly all data of a technical nature involve approximate numbers. That is numbers determined as a result of some measurement process, as with a ruler. No measurement can be found exactly.

64 Calculations with Measurements
The sum or difference of measurements can be no more precise than the least precise measurement. 42.28 mm Using a micrometer 54 mm Using a ruler, Precision of the ruler is 1 mm But actually it can be anywhere between to mm This means that the tenths and hundredths digits in the sum mm are really meaningless, the sum should be 96 mm with a precision of 1 mm

65 Calculations with Measurements
The sum or difference of measurements can be no more precise than the least precise measurement. Round the results to the same precision as the least precise measurement. 42.28 mm Using a micrometer 54 mm Using a ruler, Precision of the ruler is 1 mm But actually it can be anywhere between to mm This means that the tenths and hundredths digits in the sum mm are really meaningless, the sum should be 96 mm with a precision of 1 mm

66 Calculations with Measurements
The product or quotient of measurements can be no more accurate than the least accurate measurement. Round the results to the same number of significant digits as the measurement with the least number of significant digits. Length of a rectangle is 54.7 m Width of a rectangle is 21.5 m Area is m2 Area should be rounded to 1180 m2 To express with same accuracy

67 Rounding Numbers To round a number to a particular place value:
If the digit in the next place to the right is less than 5, drop that digit and all other following digits. Replace any whole number places dropped with zeros. If the digit in the next place to the right is 5 or greater, add 1 to the digit in the place to which you are rounding. Drop all other following digits. Replace any whole number places dropped with zeros

68 Special case, Rounding Numbers
If the digit in the next place to the right is exactly 5, add 1 to the digit in the place to which you are rounding if the previous digit is an odd number other wise just drop the digit. Replace any whole number places dropped with zeros. This rule means that if the digit to be dropped is 5 followed only by zeroes, the result is always rounded to the even digit. The rationale is to avoid bias in rounding: half of the time we round up, half the time we round down.

69 Examples of Rounding

70 Add the Measurements 1250 cm, 1562 mm, 2.963 m, 9.71 m
Convert all measurements to the same units. In this case m will be the best choice of units. 1250 cm = 12.5 m 1562 mm = m 12.5 m 1.562 m 2.963 m 9.71 m m Round to ?  Should we round before adding?

71 Calculations with Measurements
A rectangular has dimensions of 15.6 m by 11.4 m. What is the area of the rectangle? A = L x W = 15.6 m x 11.4 m = m2 = ? m2

72 Calculations with Measurements
A rectangular plot of land has an area of m2. one side has a length of 654 m. What is the length of the second side? A = L x W W = A/L = m2 / 654 m = m = ? m

73 Calculations with Measurements
Subtract the measurements: 2567 g – 1.60 kg Express your answer in g. Convert all measurements to the same units. 1.60 kg = 1600 g 2567 g 1600 g 970 g Round to ?  Should we round before subtracting?

74 Calculations with Measurements and Exact numbers
To round the result of a calculation use the precesion and the accuracy of the measured number not the exact number.

75 Calculations with Measurements and Exact numbers
2 equal rectangular plots of land has an area of 75 m2. What is the area of one plot? Area of one plot = Total Area / 2 = 75 m2 / 2 = 37.5 m2 = ? m2

76 So far… Accuracy and precision Exact number and Approximate number
Estimate Rounding USCS (United States Customary System) Systeme International (SI) or Metric system Quantities, units and symbols of the SI system Prefixes of SI system Major advantage of the SI system (multiples of 10)! Take a 10 minute break and come back at X and we’ll get started on solving equations and conversions.


Download ppt "Measurement and The Metric System"

Similar presentations


Ads by Google