What is physics?

Einstein: “physics is nothing more than refinement of everyday thinking.” Refinement: using mathematics to construct models and theories to explain and predict interactions between matter and energy. We will move from “everyday thinking” to the “refinement of everyday thinking”. • this is scientific inquiry: the systematic process of gathering data through observation, experimentation, organizing data, and conclusions.

What is physics? (mind map) • equations • hard • scientists • forces • mathematics • concepts • ideas • principles This course will give you an idea of the way physicists see the world. What is physics?

• the branch of knowledge that studies the physical world. • it can be described by a small number of relationships or

laws. These laws are usually expressed using mathematics.

Science and technology constantly interact. • new equipment produce further scientific results. • other times, science results in new products We need an understanding of physics as well as other sciences to make informed decisions involving our society.

•Discuss the difference between science and technology. Some questions to consider: •What is the moral role of scientists as they do research? •What will happen as the percentage of older people increase in our society? •Why has the state of the environment suddenly become such a big issue? Make a list of positive and negative contributions of science.

Units

• the world-wide scientific community uses the metric

system to make measurements. (SI) • related by powers of 10. • time, s • length, m • mass, kg • because other quantities can be described using these

three units, they are called fundamental units. (see below)

• derived units are combinations of fundamental units. ie.

m/s

Following are the official definitions of the seven base units, as given by BIPM. distance - meter (m) "The meter is the length of the path traveled by light in vacuum during a time interval of 1/299 792 458 of a second." mass - kilogram (kg) "The kilogram is equal to the mass of the international prototype of the kilogram." time - second (s) "The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom." electric current - ampere (A) "The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 Å~ 10-7 newton per meter of length." temperature - Kelvin (K) "The Kelvin is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water."

amount of substance - mole (mol) "The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles." intensity of light - candela (cd) "The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 Å~ 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian."

Scientific Notation

• scientists work with very small and very large numbers. • in scientific notation, the numerical part of the

measurement is expressed as a number between 1 and 10 multiplied by a whole number power of 10.

M x 10 n 1 ≤ M <10

3.88 x 103 m 487392 kg Move decimals to left

← get a large exponent 0.00951 s Move decimals to right → get a small (-) exponent • the metric system is a decimal system. Prefixes are used

to change SI units by powers of 10.

Measurement

Where do the quantities come from that scientists use for data?

- each scientist must know how trustworthy the data is. • every measurement is subject to uncertainty. All

instruments are subject to external influences. (Temperature, magnetic fields)

• accuracy - the extent in which a measured value agrees

with the standard value of a quantity. The accuracy is the difference between the measurement and the defined value. Parallax - the apparent shift in the position of an object when it is viewed from various angles.

• precision - the degree of exactness to which the

measurement of a quantity can be reproduced. The precision of an instrument is limited by the smallest division on the measurement scale.

Uncertainty in measurement affect the accuracy of a measurement. Precision is not because it is based on the smallest division on the instrument.

Sources of Error

- calibration - observation (parallax, ruler not straight, thermometer

touching the bottom of the container...) - temperature (wooden ruler - humidity, metal -

contraction/expansion) - magnetic fields Calculating % Error % error = absolute error x 100 % accepted value absolute error = measured value - accepted value

-------------- ------------ Take average of the lines. --------------- This becomes accepted value.

Calculating % difference % diff = |measured value - accepted value| x 100% accepted value

Ex. A student measures the acceleration due to gravity and finds it to be 9.72 m/s2. What is the % error if the accepted value is 9.80 m/ s2? % error = absolute error x 100% accepted value = 9.72 m/s2 9.80 m/s2 x 100% 9.80 m/s2 = 0.82%

Significant Digits/Figures

Because the precision of all measuring devices is limited, the number of digits that are valid is also limited. The valid digits are called the significant digits.

- they are the digits you are sure of and an estimated digit.

Rules for determining significant digits

1. Nonzero digits are always significant. 2. All final zeros after the decimal point are significant (if

they are to the right of a nonzero digit). 3. Zeros between two other significant digits are always

significant. (captive) 4. Zeros used solely for spacing the decimal point are not

significant. (place holders)

Operations

* the result of any mathematical operation with measurements can never be more precise than the least precise measurement. Addition and Subtraction - answer cannot be more precise than the least precise

number. 7.45 m + 0.003 m = 7.453 m precise to a precise to a hundredth thousandth = 7.45 m Rounding 0 - 4 round down 6 – 9 round up 5 round to the nearest even number Multiplication and Division

- after performing the calculation, note the factor with the least number of significant figures. Round the answer to this number of digits.

9.60 m ÷ 4.7632 s = 2.01545 → 2.02 m/s

Displaying Data Graphing - independent variable: one that the experimenter can control. - dependent variable: depends on the independent variable. Plotting Graphs 1. Identify the independent and dependent variables. (X-axis) (Y-axis) 2. Determine the range for the variables. 3. Decide if the origin (0,0) is a valid data point. 4. Number and label the axis. 5. Plot your data points. 6. Draw the best straight line or smooth curve that passes

through as many data points as possible. Do NOT connect the dots.

7. Give the graph a title.

Relationships • if the graph is a straight line, the dependent variable

varies linearly with the independent variable. • there is a linear relationship between the two variables. • the graph can be written as an equation: y = mx + b

Slope: the ratio of the vertical change to the horizontal change.

m = rise = ∆y run ∆x y-int: where the line crosses the y-axis

b

Interpolation and extrapolation

Interpolation – points within the range Extrapolation – points outside the range