Scientific Measurement Review. Physics 1 st Six Weeks

Transcription

1 Scientific Measurement Review Physics 1 st Six Weeks

2 An appetizer to start

3 What the TEKS say Physics (c) Knowledge and skills. (2) Scientific processes. The student uses a systematic approach to answer scientific laboratory and field investigative questions. The student is expected to: (H) make measurements with accuracy and precision and record data using scientific notation and International System (SI) units

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5 What the law says a history lesson In 1866, the Metric Act was signed into law by President Andrew Johnson legalizing the use of the metric system President Gerald Ford signed the Metric Conversion Act into law and It declared the Metric System "the preferred system of weights and measures for United States trade and commerce, but permitted the use of United States customary units in non-business activities. The legislation was sponsored by Rep. Olin Teague of Temple, Texas who was the Chairman of the US House Subcommittee that oversaw the manned missions to the Moon. 1988, the Trade and Competitiveness Act required federal agencies to use the metric system By the way, customary units are better known as the English System or Imperial System of miles, quarts, gallons, feet, inches, pounds, cups, ounces, etc.

6 What is the metric system? The first standardized system of measurement, based on the decimal was proposed in France about It was created to develop a unified, natural, universal system of measurement. In 1790 King Louis XVI of France assigned a group to begin this task. At that time, every country had their own system of weights and measures. England had three different systems just within its own borders!! In fact if you look up an old land document in Texas (or other parts of the US that used to be part of the Spanish Empire) you ll see land measured in a Spanish unit Varas which were about 33.3 inches or 0.85 m long. It was called the "metric" system, based on the French word for measure. As of 2005, only three countries, the United States, Liberia, and Myanmar, have not changed over to the metric system. The official modern name of the metric system is the International System of Units or abbreviated SI.

7 Behold! The countries of the world that still use the English System* *They re the ones in red Burma, Liberia, & The United States according to the CIA World Fact Book (accessed 9/13/2015)

8 What the law says and an example of why we have to catch up The problem is that all the acts passed thus far have been voluntary on the part of the States, counties, and the public. (The only exception is the FDA which requires dual labelling) But as the world has increasingly gone metric and the US must strive to stay competitive in industry, science, and business soon will come the time when it will be mandatory. Not converting has its costs. In 1999, NASA lost $125 million when its Mars Climate Orbiter (what was to be the first weather observer on another world) was destroyed after its altitude-control system mixed up U.S. customary units with metric units. A NASA review board found that the problem was in the software controlling the orbiter s thrusters. The software calculated the force the thrusters needed to exert in pounds of force. A separate piece of software took in the data assuming it was in the metric unit: Newtons.

9 The Metric System All measurements must have a number and a unit to make sense (Example: 150 cm). Also to avoid confusion, never leave a naked decimal point cover it up with a zero! In the United States, the most widely used standards of measurement are the English and the Metric System. The US is currently the only country in the world who still makes routine measurements using English units (feet, miles, gallons, etc.). Myanmar & Liberia claim they are in the process of converting. However, Science worldwide uses the Metric System for taking measurements. Another term for Metric Units are SI Units (from the French System Internationale or International System )

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11 Metric Base Units System The metric system is based on a base unit that corresponds to a certain kind of measurement Prefixes are added to show different multiples of the base unit Length = meter (m) Weight or Force = Newton (N) Volume = Liter (L) Energy = Joule (J) Mass = gram (g) Pressure = Pascal (Pa) Power = Watt (W) Note: Certain symbols for some bases are capitalized. In the case of the Liter it is capitalized when by itself only, that is to avoid the l being confused with a 1 (see they look alike, right!). The bases Watt, Joule, Newton, and Pascal are capitalized with or without a prefix, since they were named for people.

12 Metric Prefixes Prefixes plus base units make up the metric system Example: Centi + meter = Centimeter (which is 0.01x the meter) Kilo + Liter = Kiloliter (which is 1000x the Liter) *Note: without a prefix YOU ONLY HAVE A BASE Common Small Prefixes nano one billionth, symbol n micro one millionth, symbol μ milli one thousandth, symbol m centi one hundredth, symbol c deci one tenth, symbol d Common Large Prefixes Tera Trillion times the base unit, symbol T Giga Billion times the base unit, symbol G Mega Million times the base, symbol M kilo 1000 times the base, symbol k hecto 100 times the base, symbol h deca 10 times the base, symbol da

13 Metric System odds & ends Derived Units are units that are mathematical combinations of other units. Common examples of derived units include: Density (which is mass volume) = g/ml or g/cm 3 Pressure (force area) = N/cm 2 Speed (distance time) = cm/sec, m/sec, km/hr Momentum (mass x speed)= kg * cm/sec Note: 1 ml = 1 cc = 1 cm 3

14 What is the order of the common metric prefixes? King Henry declared bass did cost money King: kilo Henry: hecto declared: deca bass: base unit (m, L, g) does: deci cost: centi money: milli Note: In the SI System, the symbol for the prefix is added to the Symbol for the unit so that to show hundredths of a meter you d Use (hundredth) + (meter) or centimeter

15 Converting within the Metric System: Example #1 For each step to right, you are multiplying by 10 For example, let s go from kilo to milli For each step to right, you are multiplying by 10 Therefore, 1 kilogram = 10 hectograms = 100 decagrams = 1000 grams = decigrams = centigrams = milligrams

16 Converting within the Metric System: Example #2 For each step to left, you are dividing by 10 For example, let s go from centi to the base unit Therefore, 2.3 centimeters = 0.23 decimeters = meters