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: 0.002 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 (10 -15 ) 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