 Unit Outline--Topics What is Physics? Branches of Science

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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

Chapter 1 Objectives 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.

INTERNATIONAL SYSTEM OF UNITS (SI units)
Developed for the sake of consistency ease of understanding sharing data

BASE SI UNITS (standard units)
Measured quantity

DERIVED UNITS Derived Units: Combinations of the 7 base units.
Examples Area (length x width) m x m = m2 Velocity (distance/time) = m/s 50 m2 5 meters 10 meters

This chart allows students to see the original standard and the current standard.

Numbers as Measurements
Chapter 1 Numbers 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).

100 meters MEASUREMENTS the number of units or value the unit
Measurements consist of a number and a unit. Example 100 meters the number of units or value the unit

Dimensions and Units Chapter 1
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.

Chapter 1 Objectives List basic SI units and the quantities they describe. Using prefixes and powers of ten. Distinguish between accuracy and precision. Taking good measurements

Section 2 Measurements in Experiments
Chapter 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.

Chapter 1 Objectives List basic SI units and the quantities they describe. Using prefixes and powers of ten. Distinguish between accuracy and precision. Taking good measurements

Accuracy and Precision
Section 2 Measurements in Experiments Chapter 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.

ACCURACY Accuracy is the extent to which a measurement approaches the true value. Actual Time: 2:10 pm Your Time: 2:05 pm Your accuracy is off by 5 minutes

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.

Errors in Measurement Instrument error Method 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). Make sure your line of sight is directly over the measurement. Measurement methods that improve precision and accuracy, such as: -not using the end of the meter stick (as was done in the picture on the last slide) -measuring a quantity several times and averaging the results -having different people measure the same quantity and averaging the results.

these darts show good accuracy accurate
which paint ball mark is more accurate? less accurate - The bull’s eye represents the true value. - The darts represent three separate measurements

PRECISION Precision is the degree of exactness of a measurement.
Based on the scale of the measuring instrument. Smallest tick marks represent millimeters (mm)

PRECISION VS. ACCURACY A B C D A—Good precision and accuracy
B—Some accuracy and poor precision C—Good precision and poor accuracy D—Poor precision and accuracy

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

It’s better to be accurate.

Chapter 1 Objectives List basic SI units and the quantities they describe. Using prefixes and powers of ten. Distinguish between accuracy and precision. Taking good measurements

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. Ask students to suggest other examples of dimensions, specific units, and derived units. You may also want to discuss the advantages of using a common system of measurement.

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

What 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? *

What 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?

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.

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.