Introduction to Physics

What is Physics?§ Physics: the branch of science that

involves the study of the physical world; study of energy, matter and how they are related

§ Derived from the word “physike” = Greek for “knowledge of nature”

The Scientific Method§ Science is characterized by an organized approach called the

scientific method to learn how the natural world works§ Steps of the scientific method:

§ Questions, State the problem§ Form a hypothesis§ Experiment§ Collect & analyze data§ Draw conclusions

Experimental Variables§ A variable is any factor that might affect the behavior of an experiment§ There are 3 basic types of variables:

§ Control: variable that remains constant throughout the experiment§ Independent: factor that is changed or manipulated during the

experiment§ Always on the x-axis of a graph

§ Dependent: factor that depends on the independent variable§ Always on the y-axis of a graph

Theory vs. LawTheory

§ Theory: explanation of things or events based on knowledge gained from many observations and investigations

§ Not fixed; can undergo change§ Can be used to explain a law but do

not become laws

Law§ Law: statement about what

happens in nature and seems to be true all the time

§ Based on repeatable observations that have withstood the test of time and rarely, if ever, change

Mathematics & Physics

SI Units of Measurement§ Metric system; adopted by scientific community§ Uses 7 base quantities

• Length – meter (m)• Mass – kilogram (kg)• Time – seconds (s)• Temperature – Kelvin (K)• Amount of substance – mole (mol)• Electrical current – ampere (A)• Luminous intensity - candela (cd)

Metric PrefixesNAME POWER SYMBOLTera 1012 TGiga 109 GMega 106 MKilo 103 kCenti 10-2 cMilli 10-3 mMicro 10-6 µ

Nano 10-9 npico 10-12 pfemto 10-15 f

Unit Conversion§ Dimensional analysis = method of treating the units as algebraic

quantities that can be cancelled§ Used in choosing conversion factors

§ Ex: 43 km/hr to m/s43 km1 hr

1000 m1 km

1 hr60 min

1 min60 sec = 12 m/s

You Try!How many minutes are in a school year? (1 school year = 180 days)

1 school year = 259,200 minutes

Accuracy & Precision§ Accuracy: how close a measurement is to the accepted value§ Precision: how close a series of measurements are to each other

ACCURATE = CORRECT

PRECISE = CONSISTENT

Significant Figures§ When making a measurement, there are digits that are

known with certainty and a final digit which is uncertain or estimated

§ Valid digits in a measurement

Rules for Determining Significant FiguresRule Example

1. All non-zero number are significant 123 g ( 3 sig. figs.)

2. Zeros between non-zero digits are significant. 87009 m (5 sig. figs.)3. Leading zeros are not significant. 0.095897 (5 sig. figs.)4. If a number ends in zeros to the right of the

decimal point, those zeros are significant.9.000000 (7 sig. figs.)

5. Trailing zeros are only significant if there is a decimal point after it.

2000 (1 sig. fig.)2000. (4 sig. figs.)

Calculating with Sig FigsAddition and Subtraction§ Round off result to the same number of decimal places as the value with the fewest

decimal placesEx: § 3.7 5 mL 87.3 g

+ 4.1 mL - 1.6 5 g7.8 5 mL à 7.9 mL 85.6 5 g à 85.7 g

Multiplication & Division§ Round off result to the same number of significant figures as the value with the

least number of significant figures§ Ex: (2.4)(15.82) = 37.968 à 38

2sf 4sf 2sf

You Try!Carry out the following calculations. Express each answer to the correct number of significant figures.

§ a) 5.44 g – 2.6103 g = 2.83 g

§ b) (3.2 m)(11.57 m)= 37 m2

§ c) 15.0 km3.0 hr

= 5.0 km/hr

Scientific Notation§ Way to make very large or very

small numbers easy to work with

§ Numbers are written in the form M x 10n

§ M = a number greater than or equal to 1 but less than 10

§ n = a whole number

Converting into scientific notation1. Move decimal until there’s 1 digit to its left2. Places moved = exponent

§ Large # (great than or equal to 1) = positive exponent§ Small # (less than 1) = negative exponentEx:65000 kg = 6.5 x 104 kg0.0047 g à 4.7 x 10-3 g

Move decimal to the left?Add to the exponent

Move decimal to the right?Subtract from the exponent

You Try!Express the following in scientific notation.a) 2400000

2.4 x 106

b) 0.002562.56 x 10-3

c) 0.0000181.8 x 10-5

d) 571,0005.71 x 105

What about these?a) 12.3 x 104

1.23 x 105

b) 0.456 x 102

4.56 x 101

Remember:ü M = less than 10 & greater

than or equal to 1ü Move to ß = + exponentü Move to à = - exponent

Calculating with Scientific NotationMultiplication:§ The M factors are multiplied

§ The exponents are addedEx: (4.0 x 102)(2.0 x 105)

= 8.0 x 107

Division:§ The M factors are divided§ The exponents of the denominator is

subtracted from that of the numeratorEx: (5.0 x 109)

(2.0 x 102)= 2.5 x 107

You Try!Complete the following scientific notation calculations:

a) (2.13 x 102)(4.07 x 107)= 8.67 x 109

b) (3.2 x 10-2)(1.45 x 104)= 4.6 x 102

c) (8.2 x 108) / (4.1 x 103)= 2.0 x 105

d) (6.18 x 103)(2.9 x 10-2)

= 2.1 x 105

Analyzing Data & Graphs§ Graphs contain information about the relationships among variables

§ Directly proportional = As one quantity (independent variable) increases the other quantity (dependent variable) increases in proportion

§ Indirectly proportional = As one quantity (independent variable) increases the other quantity (dependent variable) decreases in proportion

§ Common relationships shown in graphs include: § Linear§ Quadratic§ Inverse

§ Able to use these models and relationships between variables to make predictions

Basic Trigonometry with Right Triangles § Trig uses proportions of sides and angles in a right triangle§ Triangles have 3 sides and their angles add up to 180 degrees

§ Right triangle = triangle with 90 angle§ Pythagorean theorem: a2 + b2 = c2

§ Key = label the sides correctly based on the angle that is being used!

Solving Physics Problems

GUESS methodG – GivenU – UnknownE – EquationS- SubstituteS- Solve

Ex: Using distance and time to find speed (distance = speed x time), determine average speed when a car travels 434 km in 4.5 h.§ Given:

distance = 434 km time = 4.5 h

§ Unknown: speed = ? km/h

§ Equation: distance = speed x time

speed =distance

time§ Substitute:

speed = distancetime = 434 km

4.5 h§ Solve:

speed = 434 km4.5 h = 98.4 km/h