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. 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

How did the metric system come about? 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.

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

SI Unit Prefixes

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)

Graduated Cylinder Flask

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.