The Science of Physics Section 1

UNIT OUTLINE--TOPICS

• What is Physics?• Branches of Science• Science Terms• Scientific models• Measuring and Units• Powers of Ten and conversions• Graphing• Experimental Design• Science vs. Technology • Analyzing in Physics

The Science of Physics Section 1Chapter 1OBJECTIVES

• List basic SI units and the quantities they describe.

• Using prefixes and powers of ten.

• Distinguish between accuracy and precision.

• Taking good measurements

• Use significant figures in measurements and calculations.

The Science of Physics Section 2INTERNATIONAL SYSTEM OF UNITS (SI

UNITS)

•Developed for the sake of • consistency• ease of understanding • sharing data

The Science of Physics Section 2

BASE SI UNITS (STANDARD UNITS)

Measured quantity

The Science of Physics Section 2

DERIVED UNITS

• Derived Units: Combinations of the 7 base units. • Examples• Area (length x width) m x m = m2

• Velocity (distance/time) = m/s

10 meters

5 meters50 m2

The Science of Physics Section 2

The Science of Physics Section 2Chapter 1NUMBERS AS MEASUREMENTS

• In SI, the standard measurement system for science, there are seven base units. • Each base unit describes a single dimension,

such as length, mass, or time.• The units of length, mass, and time are the

meter (m), kilogram (kg), and second (s), respectively.• Derived units are formed by combining the

seven base units with multiplication or division. For example, speeds are typically expressed in units of meters per second (m/s).

The Science of Physics Section 2

MEASUREMENTS

• Measurements consist of a number and a unit.

• Example

100 meters

the number of units or value

the unit

The Science of Physics Section 2Chapter 1DIMENSIONS AND UNITS

• Measurements of physical quantities must be expressed in units that match the dimensions of that quantity. • In addition to having the correct dimension,

measurements used in calculations should also have the same units.

For example, when determining area by multiplying length and width, be sure the measurements are expressed in the same units.

The Science of Physics Section 2Chapter 1OBJECTIVES

• List basic SI units and the quantities they describe.

• Using prefixes and powers of ten.

• Distinguish between accuracy and precision.

• Taking good measurements

The Science of Physics Section 2Section 2 Measurements in ExperimentsChapter 1

SI PREFIXES

In SI, units are combined with prefixes that symbolize certain powers of 10. The most common prefixes and their symbols are shown in the table.

The Science of Physics Section 2Chapter 1OBJECTIVES

• List basic SI units and the quantities they describe.

• Using prefixes and powers of ten.

• Distinguish between accuracy and precision.

• Taking good measurements

The Science of Physics Section 2Section 2 Measurements in ExperimentsChapter 1

Accuracy and Precision

• Accuracy is a description of how close a measurement is to the correct or accepted value of the quantity measured.

• Precision is the degree of exactness of a measurement.

• A numeric measure of confidence in a measurement or result is known as uncertainty. A lower uncertainty indicates greater confidence.

The Science of Physics Section 2

ACCURACY

• Accuracy is the extent to which a measurement approaches the true value.

Your Time:

2:05 pm

Actual Time:

2:10 pm

Your accuracy is off by 5 minutes

The Science of Physics Section 2

ACCURACY AND PRECISION

• Precision is the degree of exactness for a measurement.• It is a property of the

instrument used.• The length of the pencil

can be estimated to tenths of centimeters.

• Accuracy is how close the measurement is to the correct value.

The Science of Physics Section 2

ERRORS IN MEASUREMENT• Instrument error• Instrument error is caused by using measurement

instruments that are flawed in some way.• Instruments generally have stated accuracies such as

“accurate to within 1%.”• Method error• Method error is caused by poor techniques (see picture

below).

The Science of Physics Section 2

- THE BULL’S EYE REPRESENTS THE TRUE VALUE.- THE DARTS REPRESENT THREE SEPARATE MEASUREMENTS

accurate

less accurate

these darts show good accuracy

which paint ball mark is more accurate?

The Science of Physics Section 2

PRECISION

• Precision is the degree of exactness of a measurement.

• Based on the scale of the measuring instrument.

Smallest tick marks represent millimeters (mm)

The Science of Physics Section 2

PRECISION VS. ACCURACY

• A—Good precision and accuracy• B—Some accuracy

and poor precision

• C—Good precision and poor accuracy• D—Poor precision and

accuracy

A B C D

The Science of Physics Section 2

DISCUSSION QUESTION

• When shooting free throws, is it better to be precise or accurate?

The Science of Physics Section 2

• It’s better to be accurate.

The Science of Physics Section 2Chapter 1OBJECTIVES

• List basic SI units and the quantities they describe.

• Using prefixes and powers of ten.

• Distinguish between accuracy and precision.

• Taking good measurements

The Science of Physics Section 2

MEASUREMENTS

• Dimension - the kind of physical quantity being measured• Examples: length, mass, time, volume, and so on • Each dimension is measured in specific units.• meters, kilograms, seconds, liters, and so on

• Derived units are combinations of other units.• m/s, kg/m3, and many others

• Scientists use the SI system of measurement.

The Science of Physics Section 2

HOW TO MEASURE?

• Know how to operate the measuring instrument• Which unit(s) is represented?• What does each tick mark represent?• Are there multiple scales?• Did you zero out the instrument (if possible)

• Be skilled and patient enough to measure with the greatest detail possible

The Science of Physics Section 2WHAT DO THE TICK MARKS REPRESENT

ON A METER STICK?

• What unit is represented by the smallest tick mark on the meter stick?

m?

dm?

cm?

mm? *

The Science of Physics Section 2WHAT DO THE TICK MARKS REPRESENT

ON A METER STICK?

• What is the measurement?

In mm?

65 mm

In cm?

6.5 cm

In dm?

.65 dm

In m?

0.065 m?

The Science of Physics Section 2

WHY SO MANY DIFFERENT UNITS OF MEASUREMENT FOR THE SAME QUANTITY?

• Consider Mark and Suzy. They want to measure the length of a room. • The quantity they are measuring is

distance (measured quantity).• They both measure length in units of feet

(the length of one foot) This is their measuring units.• One important detail: Mark’s foot is longer

than Suzy’s foot.

The Science of Physics Section 2

WHY SO MANY DIFFERENT UNITS OF MEASUREMENT FOR THE SAME QUANTITY?

• Mark measures the length of the room. So does Suzy. Will they have the same measurement? Why or why not? Who will have the longer measurement in feet?• Mark’s measurement is 18 feet and Suzy’s is 23

feet.• The length of a markfoot is not the same as the

length of a suzyfoot.• To compare the two different measurements, one

unit must be converted into the other so that both measurements are proportional.• Standardizing units means to select either the

length of Mark’s or Suzy’s foot as the accepted length of the unit called a foot.