Let’s talk about feet……FOOT LAB!!!!

Accuracy and Precision

• The Goal

• Measure the distance across the room as precisely as you can using “feet” as your units of measurement.

• Resources

• Strip of adding machine tape

•  Your foot

How many feet: Presentation

• Be prepared to present your results to the class when called upon. I will ask you 3 questions.

• What was your method for getting the measurement?

• How did you maximize the precision? • What is your answer in feet and inches?

26 feet 2 inches

What is the difference between accuracy and precision?

• Accuracy is the real deal; the truth; the accepted value

• Precision has two meanings:– How repeatable the measurements are (range)– How small the interval of measurement is

• In the foot lab, what aspect of precision was being investigated?

• What do you think the goal is in science regarding accuracy and precision?

Which is more precise?

A B

Which is more precise?

A

B

Now you tell me…..

• What is the correct way to take and record a measurement?

Parallax and Precision

• Parallax

• What is it?

ParallaxAn apparent shift in position of an object when it is viewed from different angles

Location, location, location! Align eyes directly with indicator to increase

accuracy.

PrecisionHow long is the blue line?

0 ft 1 mm 2 mm

Always estimate one place beyond smallest interval.

What is the length of the blue line?

More measurement….looking for relationships

Measurements Qualitative measurements - adjectives Quantitative measurements – involve

actual numbers (quantities) These depend on reliability of the

measuring instrument. These depend on care with which it is

read.

What two items must one always What two items must one always include when taking a include when taking a

measurement?measurement?

Numerical PortionNumerical Portion

UnitUnit

Measurements REQUIRE Units of Measure

The standards of measurement used in science are those of the metric system.

The metric system is also known as the International System of Units (SI), established in 1960.

This system’s focus is simplicity and is based on 10 or multiples of 10.

In Physics these are the most prevalent units of length used

• cm, mm, km or mcm, mm, km or m

In Physics these are the most prevalent units of mass used

• g or kgg or kg

PrefixesPrefixes

One last thing - about ROUNDING

In Chemistry, you learned about Significant Figures, or Sig Figs. They relate to the precision of the measurement being taken.

In Physics, we won’t focus on Sig Figs as much. We will round answers to nearest tenth or possibly hundredth, so your answers will look like XX.X or XX.XX

Also, round at the end of computation only.

SCIENTIFIC METHOD

• What are the steps of the Scientific Method?– Ask a question.– Make a hypothesis, or educated guess.– Perform an experiment to test hypothesis.– Analyze the data from the experiment.– Form a conclusion. Did you prove or

disprove your hypothesis?

SCIENTIFIC METHOD

• Why do we care?– Effective in gaining, organizing, and applying

knowledge– An organized approach in studying problems

• Who is considered the “Father” of the Scientific Method?

Who is this?

• Galileo– 1600s– Founder of Scientific Method– Principle of Inertia– Father of Astronomy, Physics, Modern

Science– Controversy: Heliocentrism (opposed

Aristotle, Copernicus, and the Church)

Everyday Speak Science Speak

Fact The truth; immutable and absolute

observations with close agreement by competent observers; revisable data about the world

Hypothesis Guess, often used interchangeably with the term theory

Educated guess, based on observation, must be testable

Laws/Principles Something you don’t want to break

Generalizes a body of observations that have not been contradictedDiffers from Theory in that it does not explain why.

Theory Speculation, hypothesis, guess

Summarizes a hypothesis or group of hypotheses that have been supported with repeated testing. Valid as long as no evidence disproves it. An accepted hypothesis.

Order of Operations• When there is more than one operation

involved in a mathematical problem, it must be solved by using the correct order of operations .

• Remember, calculators will perform operations in the order which you enter them, therefore, you will need to enter the operations in the correct order for the calculator to give you the right answer.

PLEASE EXCUSE MY DEAR AUNT SALLYor just

P.E.M.D.A.S.

Parentheses

ExponentsMultiplication

DivisionAddition

Subtraction

OOO Practice Problems

18

2 x 3 =

OOO Practice Problems

18

(2 x 3) =

18

6 = 3

OOO Practice Problems

2[14 – 32] =

OOO Practice Solutions

2[14 – 32] =

2[14 – 9] =

2[5] =

= 10

DimensionalDimensional AnalysisAnalysis

• Used to convert between different Used to convert between different units of measurementunits of measurement

• This is done by multiplying by This is done by multiplying by factors of 1factors of 1

Converting up on down the metric Converting up on down the metric system using dimensional analysissystem using dimensional analysis

• What do you have?What do you have?

• What do you want?What do you want?

• Is your answer going to be larger or Is your answer going to be larger or smaller than the starting number?smaller than the starting number?

• What do you know?What do you know?

• Remember you must be able to cancel out Remember you must be able to cancel out all units except the one you want to end up all units except the one you want to end up withwith

Step 1Step 1• Write down the number and unit Write down the number and unit

that you are starting withthat you are starting with

Step 2Step 2• Find out how to arrive at your final Find out how to arrive at your final

unit by using known conversion unit by using known conversion factorsfactors

Step 3Step 3• Set up your conversion factor so Set up your conversion factor so

that the units cancelthat the units cancel

ExampleExample• Convert 5 m into km:Convert 5 m into km:

Step 1: you start with 5 m

Step 2: you need to get to kmStep 3: you know that: 1km = 1000 m

Step 4: 5 m X 1km = 1000 m

0.005m

**Always multiply every number across the top ,then multiply every number across the bottom. Finally divide the product of the top by the product of the bottom. Record number and unit.

Convert 170 cm to km.

170 cm1

Convert 170 cm to km.

170 cm m km1 cm m

Convert 170 cm to km.

170 cm 1 m 1 km1 100 cm 1000 m