Today’s Agenda Do Now Going over Homework Measurement Powerpoint Measurement Lab Follow-up questions Homework for next class will be to complete the follow-up questions about measurement.

Measurement in Science These slides are available to view and download on Mr. Kane’s teacher page under the name “Measurement in Science 2”

Systems of Measurement In the United States, we normally use the United States Customary System (USCS), which is also known as the British system. We also use Système International (SI) d’ unitès, which is also called the metric system. For example, if you went to the store and were going to buy a bottle of Pepsi for your family, what size bottle would you buy? Is that USCS or SI? If you went to the store to buy some milk for your family, what size bottle would you buy? Is that USCS or SI?

Measurement in Science In Science we normally use the SI system. This allows scientists all over the world to understand the measurements that other scientists make when conducting an experiment. Short ton, long ton, metric tonne Ever make a $328 million measurement error? NASA did with the Mars Climate Orbiter.

Measurement Basics Every measurement consists of a value and a unit, which is normally represented by a symbol. It is essential that you include units in ALL of your measurements.

Temperature (official) Temperature (common) Volume Amount of substance SI Units Mass Length Temperature (official) Temperature (common) Volume Amount of substance Electrical current Electrical voltage kilogram (kg) meter (m) kelvin (K) degree Celsius (°C) liter (l) mole (mol) ampere (A) volt (V)

SI prefixes Prefix Symbol Amount Number Scientific Notation µ tera T trillion 1,000,000,000,000 1 X 1012 giga G billion 1, 000, 000, 000 1 x 109 mega M million 1, 000, 000 1 x 106 kilo k thousand 1, 000 1 x 103 hecto h hundred 100 1 x 102 deka da ten 10 1 x 101 STANDARD one 1 1 x 100 UNIT (SU) deci d tenth 0.1 1 x 10-1 centi c hundredth 0.01 1 x 10-2 milli m thousandth 0.001 1 x 10-3 micro µ millionth 0.000001 1 x 10-6 nano n billionth 0.000000001 1 x 10-9

Making Precise Measurements When taking a measurement, you record every known digit and estimate the first unknown digit

Making Precise measurements 1.00 cm 1.15 cm

Making Precise measurements 1.00 cm 1.2 cm

What if the measurement falls on a line? 1.00 cm 1.50 cm

1 cm Why is it 1.50 cm? Because you estimated a digit. It is important to report the best precision that your measuring device allows.

1.40 cm 3.00 cm 1.23 cm

Confused about estimating a digit? Use this trick! If you are unsure about how many digits you should report in a measurement, just pick a spot on your measuring tool that is not on any one of the lines. Make your measurement and look at how many digits you have. Then, when you use that tool later, use the same amount of digits each time!

2.63 cm = 2 decimal points

3.00 cm = 2 decimal points

Measuring volume The same rules for precision apply: record all known digits and estimate the last one

Measure on a flat surface and at eye level

Mercury produces a convex meniscus Water produces a concave meniscus

Measuring at the meniscus

Mass on a triple beam balance

Record all known digits and estimate the last one

What about digital readers?

You cannot estimate any digits – the scale does that for you

But remember to report all the digits the scale shows you

Making unit conversions Converting from one unit to another in science is an important skill. One method that includes values from 1000 to 1/1000 involves just moving the decimal point and using a simple pneumonic. For example, what if I asked you how many mm were in 12.45 cm?

Conversions First, you use the following pneumonic to remember the first letter of the prefixes: Kangaroos Have Dirty Underwear Don’t Check Mine kilo- hecto- deka- unit deci- centi- milli- k h da u d c m Next, figure out what unit you have and what unit you want. Note the number of places you have to move over and which direction. Then, move the decimal that number of times in that direction.

How many mm are in 12.45 cm? kilo- hecto- decka- unit deci- centi- milli- k h da u d c m You have to move one to the right to go from centi- to milli-. So move the decimal point one to the right. So, 12.45 cm = 124.5 mm What if I asked you how many meters were in 5.34 kilometers? 5.34 kilometers = 5340 meters (move the decimal 3 places to the right)

Using conversion factors Another way of converting units is using conversion factors. You do this all the time. For example if I asked you how many eggs are in 2 dozen, what would you say? There are 24 eggs in 2 dozen. You used the following conversion factor to determine this: 2 dozen X 12 eggs = 24 eggs dozen

Conversion factors Conversion factors are based on the principle that you can multiply anything by 1 and not change its value Here is what you generally need to do: What you have X unit you want = unit you have Remember that (unit you want / unit you have) must = 1 Try to figure out how many seconds are in 24 hours.

Precision vs. Accuracy Example: a 100-meter dash is timed by four different judges. Here are the results: Judge 1 9.58 s Judge 2 9.6 s Judge 3 11.5 s Judge 4 10 s Which is the most precise measurement? Which is the least accurate? Judge 1 Judge 3

Precision vs. Accuracy Judge 1 9.58 s Judge 2 9.6 s Judge 3 11.5 s Accuracy is how close the measurement is to the actual value. Because Judge 3 had a time that was significantly different than the others, we can assume that her time was inaccurate. Precision is a gauge of how exact a measurement is. Therefore, the most precise measurement was taken by Judge 1. Anyone know a person who can run that time in 100 meters?