WHAT IS PHYSICS, MEASUREMENT AND UNCERTAINTY?

Topics 1.1 and 1.2 on IB Syllabus

What is Physics? What are the topics of Physics?

What does physics have to do with me?

Discussion: Identify the area of physics that is most relevant to each of the following situations:

1.Lighting in your room2.Listening to your favorite band3.Wearing sunglasses4.A soccer game5.Cooking dinner

What range of sizes does the universe hold? Powers of 10 Videohttps://www.youtube.com/watch?v=0fKBhvDjuy0

A power of 10 (102, 105 , 10-12) are called orders of magnitudes

Ranges:

Length: radius of the observable universe

(13.7 billion light years)

diameter of proton

Mass: total mass of observable universe mass of an electron

• Time: age of the universe passage of light across a

nucleus

2610 m

1610 m

5210 kg3210 kg

2010 s2410 s

How do we measure and express measurement in physics?1. Fundamental Units2. Derived Units

1. Fundamental Units

http://www.unc.edu/~rowlett/units/sifundam.html

2. Derived Units

Examples:

A Newton:

A Watt:

How do we convert between units? Convert a posted speed limit in the

US of 55 miles/hour into Meters per second Kilometers per hour

• Helpful Conversions:• 1.6 km/mile

SI Unit Prefixes:

See your textbook pg. 12 for common prefixes.

• How many kisses is 50 kilo kisses?• What would you be if you earned 7

megabucks a year?

1012 Microphones = 1 megaphone500 millinaries = 1 seminary2000 mockingbirds = 2 kilomockingbirds10 cards = 1 decacards10-6 fish = 1 microfiche1021 picolos = 109 los = 1 gigolo10 rations = 1 decoration10 millipedes = 1 centipede2 snake eyes = 1 paradise2 wharves = 1 paradox10-6 phones = 1 microphone106 phones =1 megaphone10-2 mental = 1 centimental10-1 mate = 1 decimate1012 bulls = 1 terabull10-12 boos = 1 picoboo10-15 bismol = 1 femtobismol

Measurement, Precision and Accuracy

How do we represent precision?

Significant Figures The number of significant digits in a measured value indicates the

precision of that measurement – a reading of 123.45 g is more precise than a reading of 123 g. To determine the number of significant digits in a number:

read the number from left to right the 1st significant digit is the 1st non-zero number you find that digit and all that follow are significant provided there is a decimal

point (if there is no decimal point and the number ends with 0’s, don’t count them)

in proper scientific form, all numbers in front of the 10 are significant

eg. 30.400 has 5 significant digits0.1620 has ____ significant digits0.030 has ____ significant digits400 has ____ significant digit400. has ____ significant digits 4.0102 has ____ significant digits

Calculations with Sig Figs

ADDITION RULEThe sum of the numbers cannot be more

precise than the least precise number. You do not really use significant digits.

Calculations with Sig Figs

The product cannot be greater than the number of significant figures in the factor having the fewest significant figures.

What is the difference between precision and accuracy?

Precision vs. Accuracy

Accuracy:

Precision:

Precision vs. Accuracy

Label each of the ducks with the either: High Accuracy, High precision High Accuracy, Low precision Low Accuracy, High precision Low Accuracy, Low precision

Precision vs. Accuracy

Systematic Errors… affect accuracy

Systematic Errors… affect accuracy

The precision of the tool often determines the precision of data taken

Compare these two measuring tools: What is the reading of the purple line?

*** Always estimate to the smallest division plus one more decimal point

Random errors… affect precision. Example: Three

people time how long it takes to drop a ball from shoulder height.

Data:

Just because a tool is precise (timer) doesn’t mean that the measurements taken are precise. ground.

Even though a timer is precise, there is random error in this experiment, which affects precision.