Chapter 1

The Science of Physics

Key Objectives

•Definition of Physics

•Areas within Physics

•Scientific Method

•Measurements and Units (SI)

•Accuracy and Precision

•Dimensional Analysis

Definition of Physics Physics is the study

of the physical world.

Physics can be used to explain every object and phenomena around you.

Areas of PhysicsName Subjects

Mechanics

Thermodynamics

Vibrations and Waves

Optics

Electromagnetism

Relativity

Quantum Mechanics

Motion and its causes

Heat and Temperature

Specific types of repetitive motion

Light

Electricity, Magnetism, & Light

Particles moving at high speeds

Behavior of submicroscopic particles

Accuracy v PrecisionAccuracy ishow close a measured value is to the true value or accepted value.

Precision is

How close each measurement is to each other measurement.

Our goal is to be both accurate and precise in our measurements.

Significant FiguresIn order to be accurate and precise with our measurements, we must pay attention to significant figures while analyzing data on the calculator.

The numbers

1 2

3

4

5

6

7

8

9

count as significant figures

0 is a significant figure under certain conditions

•It is used after a decimal point to show accuracy of measurement

4.2300

•It is trapped between other significant figures.

2804

0 is not a significantfigure if

•It is used as a place holder between significant figures and the decimal.

430 .0222

Addition & SubtractionTo determine the number of significant figures you can keep when you are adding/subtracting measurements, you need to look at the least accurate measurement.

That means the number showing the least amount of digits as you move right through the number. For instance:

46.4 Shows that we are accurate to the tenths place.

9.46 Shows we are accurate to the hundredths place.

270 Shows we are accurate to tens place!+

When we add those together325.86

We can only keep to the tens place.330

Multiplication & DivisionFinding how many significant figures to keep with multiplication and division is much easier than with other operations.

That is because you simply count how many significant figures are in each measurement, and keep the number of significant figures equivalent to the measurement with the least number.

46.40 Has 4 significant figures.

120.46 Has 5 significant figures

27.1 Has 3 significant figures.

So when we multiply these together.

x151471.2224

We can only keep 3 significant figures151,000

What is the Scientific Method?

There is no single procedure that scientists follow in their work. But, there are certain steps common to all good scientific investigations. Those steps are called the scientific method.

ObservationGather information that would lead to you to a question.

Hypothesis

Experiment

Make an educated guess for an answer to your question

ConclusionPerform an experiment and collect data to support your hypothesis.

Make a final statement based on your findings to prove your hypothesis.

Units of MeasurementThere are many different systems of measurements in science.

Here in the United States, we use the English system of units.

miles pounds Fahrenheit

Other countries, such as Canada, use the Metric system of units.

meter gram Celsius

Since the world cannot decide on what units to use, scientists have. We have come to a mutual agreement for a consistent system of units . . .

SI UnitsThat mutual system is called the International System of units. We abbreviate it using SI, which is short for Systeme International.

Quantity Unit

Length meter (m)

Mass kilogram (kg)

Temperature kelvin (K)

Time second (s)

Current ampere (A)

Energy joule (J)

Force newton (N)

Standards of Length, Mass, and Time

We all know these are used to measure certain characteristics of the phenomena around us.

Before we knew of things such as the meter, or kilogram, or second, the quantities above had no standard way of being measured.

So how did we come to designate a certain distance, or time interval, or mass as being the standards for all measurements?

The Meter The meter was originally defined in France as one ten-

millionth of the distance from the Equator to the North Pole. Until 1960, the meter was defined by the distance between

two lines on a specific bar of platinum-iridium alloy.– Kept in the National Institute of Standards and Technology in

Sèvres, France. In 1983 the meter took on the current definition as the

distance traveled by light in a vacuum during the time interval of1/299,792,458 second.– vlight = 299,792,458 m/s

v = fλ– λ = 1 / 299,792,458

The Kilogram

The kilogram is defined as the mass of a specific platinum-iridium alloy cylinder kept as the International Bureau of Weights and Measures in Sèvres, France.– Platinum-Iridium alloy is a very stable metal with

no tendency to rust or be chemically altered by its environment.

– It is a disadvantage to maintain a measurement that way because it is only accessible to those in the institute.

So any other kilogram measurement is accepted to be so.

The Second

Before 1960, the time standard was defined as the average length of a solar day in the year 1900.– A solar day is the time interval between successive

appearances of the Sun at its highest point each day. So that would be 1 / 86,400 of a day!

In 1967, we were able to take advantage of new technology in the atomic clock.– A clock that uses the frequency of the light emitted from

the cesium-133 atom. The second is now defined as 9,192,631,700 times

the period of oscillation of radiation from the cesium atom.

Dimensional AnalysisThe is a term given to the process for converting units from system to system, or even within the same system.

You goal is to use conversion factors to cancel out the units you no longer want, and create the units for your new measurement.

Some conversion factors are:

1 in = 2.54 cm

1 kg = 2.2 lbs

1 oC = 9/5(oF) + 32

1 km = 0.62 mi

PrefixesPrefix Symbol Number

pico-

nano-

micro-

milli-

centi-

deci-

kilo-

mega-

giga-

p

n

μ

m

c

d

k

M

G

.000000000001

.000000001

.000001

.001

.01

.1

1000

1,000,000

1,000,000,000

Converting UnitsTime to try a couple of conversions.

Convert 7.35 in to cm First write down your given information

7.35 in Then multiply by conversion factor.

X 2.54 cm

1 in

Notice the unit we want to go away is put on the bottom so it divides out!

Now multiply/divide the numbers as shown.

18.669

Label with the units that are left over.

cm

Don’t forget significant figures!

18.7 cm

Another ExampleTry one that is a little tougher and involves multiple steps.

Convert 75 mph to m/s.

75 mph 1 km

0.62 mi

1000 m

1 km

1 h

60 min

1 min

60 s

x x x x = 33.60215

34 m/s

Interesting FactsMeasurement Value

One light-year 1 x 1025 m

Mean distance from Earth to Moon

4 x 108 m

Mean radius of Earth 6 x 106 m

Size of cells of most living organisms

1 x 10-5 m

Diameter of a proton 1 x 10-15 m

Average age of a college student

6 x 108 s

Time between normal heartbeats

8 x 10-1 s

Duration of a nuclear collision 1 x 10-22 s

Building Blocks of Matter We all know that matter is made of

many small particles called atoms. We also know that atoms are made of

even smaller particles called protons, neutrons, and electrons.

But what are protons, neutrons, and electrons made of?

Quarks Quarks are particles that make up the more commonly known

particles called protons, neutrons, and electrons. There are six particles that are defined as quarks.

– They are named as follows:1. Up2. Down3. Strange4. Charmed5. Bottom6. Top

The up, charmed, and top quarks have a charge +2/3 that of a proton.

So a proton consists of two up quarks and one down quark. The down, strange, and down quarks have a charge of –1/3 that of a

proton. A neutron consists of two down quarks and one up quark.

Coordinate Systems We are able to model position and

distance by using a coordinate system to graph our model.

There are two types of systems– Cartesian coordinate

X-Y Axis

– Plane polar

Plane Polar A plane polar system only needs an origin and a

line of reference. The coordinates for any point refer to the

distance from the origin and the angle of rotation from the line of reference.– A counter-clockwise rotation gives a positive angle of

rotation.– A clockwise rotation gives a negative angle of rotation.

The coordinates are labeled…– (r , θ) where r is the distance from the origin and θ is

the angle of rotation.

Converting Between Systems

Knowing the polar coordinates, we can convert using one simple transformation– (r , θ) (r cos θ , r sin θ) (x , y)

Knowing the Cartesian coordinates, the transformation is a little more complicated– (x , y) (√x2+y2 , tan-1 y/x) (r , θ)