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Measurement & Scientific Tools. Description vs. Explanation. Description : a spoken or written summary of observations Explanation : an interpretation of observations. Measurement. Must have a standard. A standard is an exact quantity people agree to use for comparison .
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Description vs. Explanation • Description: a spoken or written summary of observations • Explanation: an interpretation of observations
Measurement • Must have a standard. • A standard is an exact quantity people agree to use for comparison. • That means two people using the same object should get close to the same results.
Standards of the past • People used to use parts of their body to determine the length of something. • The standard would be a part of the king’s anatomy. • The standard yard was the distance from the king’s nose to his outstretched arm
People would use their feet to measure distance • This is how the term foot came about. • Today the standard “foot” in the English system is • 12 inches = 1 foot
The English system is very confusing because it has so many different values
America is the only country that still uses the old English system
During the18th century scientists measured the distance from the earth’s equator to its North Pole and divided it into ten million parts. This is how they came up with the length of the standard meter. How did the metric system come about?
The Meter • The standard for the meter is kept in a safe in France. • The meter stick is a replica of that standard • A meter is made up of 100 centimeters and 1000 millimeters
The Metric System • International System of Units (SI) • The internationally accepted system of measurement
Accuracy, Precision, and Error • It is necessary to make good, reliable measurements in the lab • Accuracy – how close a measurement is to the true value • Precision – how close the measurements are to each other (reproducibility)
Precision and Accuracy Precise, but not accurate Neither accurate nor precise Precise AND accurate
Scientific Notation (4.2 x 105) • Astronomically Large Numbers • mass of planets, distance between stars • Really Really Small Numbers • size of atoms, protons, electrons
How to Write in Scientific Notation • Move decimal until number is between 1 and 10. • Count the number of decimal places moved and take note of the direction. • Rewrite the number without extra zeros. • Write a x symbol and 10 with an exponent equal to the number of decimal places moved. • 428,500 4.285 x 105(decimal moves 5 spots left) • 0.0004285 4.285 x 10-4(decimal moves 4 spots right)
Powers of 10 • Positive Exponents
Powers of 10 • Negative Exponents
Converting from Scientific Notation back to Standard • Move decimal point same # of spaces as the exponent on the 10 • If exponent is positive, move decimal to the right • If exponent is negative, move decimal to the left • 4.285 x 102 428.5(move decimal 2 spots right) • 4.285 x 10-4 0.0004285(decimal moves 4 spots left)
Microscope • A tool that magnifies at a much higher power than a hand lens. • It magnifies smaller objects or makes smaller objects larger.
Meter Stick • A meter tool that is used to measure distance and the length of objects. • It tells how long an object is. • What is the SI unit? • Meter (m)
Thermometer • A tool used to measure temperature. • What is the SI Unit? • Celcius (C)
Balance • A tool used to measure the mass of an object. • What is the SI unit? • gram (g) • A balance tells the amount of matter an object contains.
Spring Scales • Springs Scales measure weight in Newtons (N) • What is the difference between weight and mass? • Weight is the gravitational pull on an object
Beaker • An open cylindrical container with a pouring lip. • It measures volume. • What is the SI unit? • Liter (L)
Tools & Accuracy • Are measurements with tools exact? • Accepted value – The actual scientific value of a measurement. • Percent Error – the expression of error as a percentage of the accepted value.
