a physics toolkit

A Physics ToolkitChapter 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 (1012)

• 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 = ax2 + 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