Happy Tuesday! 10 minutes to finish metric measurement lab We will go over lab/questions Notes: measurement and units Quiz Friday 1 st Test: September 10 th

Metric Money

Money uses the metric system: $1 is the basic unit of money in the USA, just as the meter is the basic unit of length in the metric system.

By the way, make sure you always use the cm side of the meter stick, not the inches side!

All amounts of money are written relative to the dollar, just as all lengths are written relative to the meter.

Example: A centimeter = 1/100 of a meter, or 0.01 meters. A “centidollar” is 1/100 of a dollar, or $0.01, which is 1¢.

A “decidollar” is 1/10 of a dollar. We call that a “dime”. What is a “kilodollar”? Do we ever write it that way?

Sometimes salaries are printed like this: “Joe earns $55 k/yr.” This means that Joe earns 55 kilodollars per year. Which means $55,000.

Actual internet job listing!

In sports, if an athlete signs a contract for $5,700,000 they usually don’t print all those zeroes in the newspaper. Instead, they write “$5.7M” or “$5.7M/yr.” “M” is the metric prefix for “Mega”. Mega means “million”!

Actual business headline!

Isn’t this a silly name for the lottery?

“Megamillion” means “a million million” …. Which is a TRILLION!

“cheese queso”?

Key conversions Kilo = 1000 Centi = 1/100 Milli = 1/1000

The Uses of Numbers

THE BIG THREE THE THREE MAIN UNITS WE USE IN PHYSICS ARE: METERS KILOGRAMS SECONDS

How good are the measurements? Scientists use two words to describe how good the measurements are: 1. Accuracy – how close the measurement is to actual value 2. Precision – how well the measurement can be repeated

Accuracy & Precision…the differences Accuracy Can be true of a single measurement OR of multiple trials Precision MUST have multiple trials before anything can be said about it The smaller a measuring tool measures, the more precise its measurements are said to be

Accuracy is like telling the truth Precision is telling the same story over and over again.

Precision

accuracy

Precision and accuracy

Let’s use a golf analogy

Accurate?No Precise?Yes

Accurate?Yes Precise?Yes

How to find out whether something is accurate or precise? Accurate: find the average Precise: find the range (find the difference between the highest and lowest number) It is accurate it average is less than one away from accepted avg. It is precise if the range is less than 1

Data Table: Boiling Point of Water ReadingThermometer 1Thermometer 2Thermometer 3Thermometer °C97.5°C98.3°C97.5°C °C102.3°C98.5°C99.7°C °C 99.7°C 98.4°C96.2°C °C100.9°C98.7°C94.4°C Average °C 100.1°C 98.5°C 97.0°C Range Accurate? Precise? 0.2 yes 4.8 yes 0.4 no 5.3 no

Question: Suppose that you do a lab experiment to measure the acceleration due to gravity. Four different measurements give the answers of 9.9 m/s 2, 10.2 m/s 2, 9.7 m/s 2 and 10.1 m/s 2. The actual value of gravity on Earth is 9.8 m/s 2. Are your measurements precise? Yes: the range is 0.5 Are they accurate? Yes: the average is 10, which is only 0.2 away from the actual value

Question: You and a group of friends are trying to measure how many jellybeans will fit in an empty peanut butter jar. You find that 738 fit in your jar. Friend #1 finds that 1135 fit in his jar, and friend #2 finds that 1304 fit into her jar. According to your teacher (who is never wrong!) the answer should be “about 900”. Are your group’s measurements precise? No Are they accurate? No

PRACTICE

Use your white board to answer the following: Place the following metric prefixes in order from SMALLEST to LARGEST: Kilo, base, Mega, milli, centi, micro Ans: micro, milli, centi, base, kilo, Mega How many seconds are there in 2 years? Ans: seconds

Calculate: The perimeter of an irregularly shaped object whose sides are m, m, m, and 68.4 m. A B. 482 C Ans: C When adding, go with the number that is the LEAST PRECISE, meaning it has the fewest number of digits after the decimal

SI Units: Système Internationale d’Unités SI Base Units For Physics Time- seconds (s) Length- meters (m) Mass- kilograms (kg)

Scientific Notation Review And the metric system!

Name those sig figs!