A Physics Toolkit Chapter 1

1.1 Physics Energy, matter and their relationship Understanding the physical world Careers –Scientists, astronomers, engineers, teachers, computer science, medicine

Mathematics Language of physics Model observations Representations –Equations, pictures, force diagrams, written descriptions, motion maps…

DOES IT MAKE SENSE?? Numbers, units, blah, blah, blah Copper ball falls 5 m. –Calculated answers: s or 17 s

SI Units 7 base units: Meter, Kilogram, Second, Kelvin, Mole, Ampere, Candela Everything else is derived –Joule –Coulomb –Newton

Conversions Femto ( ) to tera (10 12 ) Same as chemistry Dimensional analysis –1kg/1000g = 1

Significant Figures Zeros to locate the decimal are not significant Scientific notation makes it easier to identify significant zeros Arithmetic result may never be more precise than the least precise measurement –Addition, subtraction, multiplication, division Counting numbers are exact

Scientific Methods Make observations Do experiments Create models or theories to explain results Repeat for many iterations How are variables related?

MODELS, Laws, Theories Models based on experimentation –Atomic model, Bohr model, Quantum model New data that doesn’t fit existing model –Evaluate both data and model Reproducibility of data Validity of model

Models, LAWS, Theories Rule of nature Sums up related observations Describes pattern in nature –Conservation laws, Law of reflection Do NOT explain why things happen

Models, Laws, THEORIES Explanation based on many observations Based on experimental results May be explanations of laws Only a well supported explanation Theory of Universal Gravitation, Atomic Theory

1.2 Measurement Comparison between a standard and unknown quantity Often reported with uncertainty If values overlap within uncertainty, data agrees –Figure 1-10, pg 12

PRECISION versus Accuracy Degree of exactness of measurement –Smallest amount of uncertainty is most precise Depends on instrument and technique Finest division on device Precision is ½ smallest division –Graduated cylinder with 1 mL division –Beaker with 50 mL division Shown by significant figures

Precision versus ACCURACY Describes how well measurements agree with the accepted value Real value versus Accepted value –Can you ever know the exact measurement? Yes and no

Good Measurements Read measurements at eye level –Reduces error caused by parallax Carefully Multiple times as necessary Correct device for type of measurement

1.3 Graphing Data Represent relationships between variables Independent variable is manipulated Dependent variable responds Rule of One

Line of Best Fit Best model of the data Drawn close to all data points possible Problem-solving strategies, pg 16

Linear Relationships Dependent variable varies linearly with independent variable Relationship is y=mx+b Use points on the line of best fit to calculate slope and y-intercept Slope = change in y over change in x

Nonlinear Relationships Quadratic –y = ax 2 + bx + c –One variable depends on the square of another Inverse (hyperbola) –y = a/x –One variable depends on the inverse of the other Others

Predicting Values Can use the graph to make predictions –Interpolation –Extrapolation Can use the equation for the graph to make predictions

Lab Graphing activity – after finishing slides Vernier Caliper lab – after section 2 discussion